Securities - Pre-Tax Net Securities Gains (Losses) by Type (Details) - USD ($) $ in Millions	3 Months Ended			6 Months Ended
	Jun. 30, 2020	Mar. 31, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Total net securities gains (losses)	$ 9	$ 9	$ 7	$ 18	$ 8
Supranational
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Total net securities gains (losses)	6	0	0	6	0
U.S. Treasury
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Total net securities gains (losses)	1	5	3	6	4
Other
Schedule of Investment Income, Reported Amounts, by Category [Line Items]
Total net securities gains (losses)	$ 2	$ 4	$ 4	$ 6	$ 4