AFS and HTM Debt Securities, Credit Loss Component (Details) - Debt securities [Member] - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Other than Temporary Impairment, Credit Losses Recognized in Earnings [Roll Forward]
Credit loss recognized, beginning of period	$ 232	$ 649	$ 562	$ 742
Additions:
For securities with initial credit impairments	4	0	6	0
For securities with previous credit impairments	3	8	17	17
Total additions	7	8	23	17
Reductions:
For securities sold, matured, or intended/required to be sold	(23)	(30)	(369)	(131)
For recoveries of previous credit impairments	0	(1)	0	(2)
Total reductions	(23)	(31)	(369)	(133)
Credit loss recognized, end of period	$ 216	$ 626	$ 216	$ 626