AFS and HTM Debt Securities, OTTI Debt Securities (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Debt securities [Member]
OTTI on debt securities (Abstract)
Total recorded as part of gross realized losses	$ 5	$ 7	$ 23	$ 107
Total changes to OCI for non-credit-related OTTI	(5)	(2)	(9)	(53)
Total OTTI losses (reversal of losses) recorded on debt securities	0	5	14	54
Securities of U.S. states and political subdivisions [Member]
OTTI on debt securities (Abstract)
Total recorded as part of gross realized losses	0	1	2	9
Total changes to OCI for non-credit-related OTTI	0	0	(2)	(5)
Residential [Member]
OTTI on debt securities (Abstract)
Total recorded as part of gross realized losses	0	1	2	7
Total changes to OCI for non-credit-related OTTI	0	(1)	(1)	(1)
Commercial Mortgage Backed Securities [Member]
OTTI on debt securities (Abstract)
Total recorded as part of gross realized losses	1	4	15	70
Total changes to OCI for non-credit-related OTTI	(5)	0	(6)	(47)
Corporate debt securities [Member]
OTTI on debt securities (Abstract)
Total recorded as part of gross realized losses	0	1	0	21
Total changes to OCI for non-credit-related OTTI	0	0	0	1
Other [Member]
OTTI on debt securities (Abstract)
Total recorded as part of gross realized losses	4	0	4	0
Total changes to OCI for non-credit-related OTTI	0	(1)	0	(1)
Credit-related OTTI [Member] | Debt securities [Member]
OTTI on debt securities (Abstract)
Total recorded as part of gross realized losses	5	6	22	105
Intent-to-sell OTTI [Member] | Debt securities [Member]
OTTI on debt securities (Abstract)
Total recorded as part of gross realized losses	$ 0	$ 1	$ 1	$ 2