Investment Securities, Credit Loss Component (Details) - Total debt securities [Member] - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Other than Temporary Impairment, Credit Losses Recognized in Earnings [Roll Forward]
Credit loss recognized, beginning of period	$ 1,120	$ 1,080	$ 1,043	$ 1,092
Additions:
For securities with initial credit impairments	0	16	8	54
For securities with previous credit impairments	6	5	97	48
Total additions	6	21	105	102
Reductions:
For securities sold, matured, or intended/required to be sold	(96)	(22)	(114)	(111)
For recoveries of previous credit impairments	(1)	(2)	(5)	(6)
Total reductions	(97)	(24)	(119)	(117)
Credit loss recognized, end of period	$ 1,029	$ 1,077	$ 1,029	$ 1,077