AFS and HTM Debt Securities, OTTI Debt Securities (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Debt securities [Member]
OTTI on debt securities (Abstract)
Total recorded as part of gross realized losses	$ 7	$ 8	$ 52	$ 18
Total changes to OCI for non-credit-related OTTI	(1)	(11)	(1)	(4)
Total OTTI losses recorded on debt securities	6	(3)	51	14
Securities of U.S. states and political subdivisions [Member]
OTTI on debt securities (Abstract)
Total recorded as part of gross realized losses	4	0	33	2
Total changes to OCI for non-credit-related OTTI	(1)	0	(1)	(2)
Residential [Member]
OTTI on debt securities (Abstract)
Total recorded as part of gross realized losses	0	1	0	2
Total changes to OCI for non-credit-related OTTI	0	0	(1)	(1)
Commercial [Member]
OTTI on debt securities (Abstract)
Total recorded as part of gross realized losses	3	7	17	14
Total changes to OCI for non-credit-related OTTI	0	(11)	1	(1)
Credit-related OTTI [Member] | Debt securities [Member]
OTTI on debt securities (Abstract)
Total recorded as part of gross realized losses	7	8	23	17
Intent-to-sell OTTI [Member] | Debt securities [Member]
OTTI on debt securities (Abstract)
Total recorded as part of gross realized losses	$ 0	$ 0	$ 29	$ 1