Guarantees and Commitments Guarantees and Commitments (Standby letters of credit and other guarantees) (Details) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Guarantor Obligations [Line Items]
Standby letters of credit and other guarantees	$ 6	$ 7
Standby letters of credit, cash collateral received	0
Maximum
Guarantor Obligations [Line Items]
Standby letters of credit and other guarantees	$ 249	$ 218