Investment Securities, OTTI Included in Earnings (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Schedule of Marketable Securities [Line Items]
Other than Temporary Impairment Losses, Investments, Held-to-maturity Securities			$ 0	$ 0
OTTI write-downs included in earnings (Abstract)
Total investment securities (1)	$ 52	$ 74	147	125
Nonmarketable equity investments (1)	84	66	317	183
Total OTTI write-downs included in earnings (1)	136	140	464	308
Total debt securities [Member]
OTTI write-downs included in earnings (Abstract)
Total investment securities (1)	51	73	142	123
Securities of U.S. states and political subdivisions [Member]
OTTI write-downs included in earnings (Abstract)
Total investment securities (1)	30	2	40	18
Residential [Member]
OTTI write-downs included in earnings (Abstract)
Total investment securities (1)	4	9	28	43
Commercial [Member]
OTTI write-downs included in earnings (Abstract)
Total investment securities (1)	10	3	11	3
Total marketable equity securities [Member]
OTTI write-downs included in earnings (Abstract)
Total investment securities (1)	1	1	5	2
Other marketable equity securities [Member]
OTTI write-downs included in earnings (Abstract)
Total investment securities (1)	1	1	5	2
Corporate debt securities [Member]
OTTI write-downs included in earnings (Abstract)
Total investment securities (1)	7	59	57	59
Other [Member]
OTTI write-downs included in earnings (Abstract)
Total investment securities (1)	0	$ 0	6	$ 0
Energy [Domain]
OTTI write-downs included in earnings (Abstract)
Total OTTI write-downs included in earnings (1)	32		185
Energy [Domain] | Investment securities [Member]
OTTI write-downs included in earnings (Abstract)
Total OTTI write-downs included in earnings (1)	6		57
Energy [Domain] | Other Assets: Nonmarketable Equity Investments [Member]
OTTI write-downs included in earnings (Abstract)
Total OTTI write-downs included in earnings (1)	$ 26		$ 128