Annual report pursuant to Section 13 and 15(d)

Variable Interest Entities (Summary of Key Terms of NMTC Transactions) (Details)

v3.10.0.1
Variable Interest Entities (Summary of Key Terms of NMTC Transactions) (Details) - Primary Beneficiary
$ in Millions
12 Months Ended
Dec. 31, 2018
USD ($)
NMTC 2  
Variable Interest Entity [Line Items]  
Loan Amount $ 37.7
Interest Rate on Loan 1.00%
NMTC 2 | Minimum  
Variable Interest Entity [Line Items]  
Interest Rate on Loan 0.71%
NMTC 2 | Maximum  
Variable Interest Entity [Line Items]  
Interest Rate on Loan 0.77%
NMTC 2 | US Bancorp  
Variable Interest Entity [Line Items]  
Financial Support to Other Entity $ 17.5
NMTC 2 | Unicom  
Variable Interest Entity [Line Items]  
Financial Support to Other Entity 52.0
NMTC 3  
Variable Interest Entity [Line Items]  
Loan Amount $ 8.2
Interest Rate on Loan 1.00%
NMTC 3 | US Bancorp  
Variable Interest Entity [Line Items]  
Financial Support to Other Entity $ 3.8
NMTC 3 | Unicom  
Variable Interest Entity [Line Items]  
Interest Rate on Loan 1.35%
Financial Support to Other Entity $ 12.0
NMTC 4  
Variable Interest Entity [Line Items]  
Loan Amount $ 6.7
Interest Rate on Loan 1.00%
NMTC 4 | US Bancorp  
Variable Interest Entity [Line Items]  
Financial Support to Other Entity $ 3.3
NMTC 4 | Unicom  
Variable Interest Entity [Line Items]  
Interest Rate on Loan 0.73%
Financial Support to Other Entity $ 9.8
NMTC 5  
Variable Interest Entity [Line Items]  
Loan Amount $ 10.4
Interest Rate on Loan 1.00%
NMTC 5 | Minimum  
Variable Interest Entity [Line Items]  
Interest Rate on Loan 0.67%
NMTC 5 | Maximum  
Variable Interest Entity [Line Items]  
Interest Rate on Loan 1.24%
NMTC 5 | US Bancorp  
Variable Interest Entity [Line Items]  
Financial Support to Other Entity $ 5.1
NMTC 5 | Unicom  
Variable Interest Entity [Line Items]  
Financial Support to Other Entity $ 14.7