AFS and HTM Debt Securities, OTTI Included in Earnings (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Schedule Of Available-For-Sale Debt Securities [Line Items]
Other-than-temporary Impairment Loss, Debt Securities, Held-to-maturity, before Tax			$ 0	$ 0
Debt securities [Member]
OTTI write-downs included in earnings (Abstract)
Total debt securities (1)	$ 7	$ 8	52	18
Securities of U.S. states and political subdivisions [Member]
OTTI write-downs included in earnings (Abstract)
Total debt securities (1)	4	0	33	2
Residential [Member]
OTTI write-downs included in earnings (Abstract)
Total debt securities (1)	0	1	0	2
Commercial [Member]
OTTI write-downs included in earnings (Abstract)
Total debt securities (1)	3	7	17	14
Corporate debt securities [Member]
OTTI write-downs included in earnings (Abstract)
Total debt securities (1)	$ 0	$ 0	$ 2	$ 0