Investment Securities, OTTI Included in Earnings (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
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)	$ 51	$ 26	104	95
Nonmarketable equity investments (1)	22	104	98	233
Total OTTI write-downs included in earnings (1)	73	130	202	328
Total debt securities [Member]
OTTI write-downs included in earnings (Abstract)
Total investment securities (1)	48	26	100	91
Securities of U.S. states and political subdivisions [Member]
OTTI write-downs included in earnings (Abstract)
Total investment securities (1)	0	6	8	10
Residential [Member]
OTTI write-downs included in earnings (Abstract)
Total investment securities (1)	3	12	6	24
Commercial [Member]
OTTI write-downs included in earnings (Abstract)
Total investment securities (1)	41	0	66	1
Corporate debt securities [Member]
OTTI write-downs included in earnings (Abstract)
Total investment securities (1)	4	5	20	50
Other [Member]
OTTI write-downs included in earnings (Abstract)
Total investment securities (1)	0	3	0	6
Total marketable equity securities [Member]
OTTI write-downs included in earnings (Abstract)
Total investment securities (1)	3	0	4	4
Other marketable equity securities [Member]
OTTI write-downs included in earnings (Abstract)
Total investment securities (1)	3	0	4	4
Energy [Domain]
OTTI write-downs included in earnings (Abstract)
Total investment securities (1)	7	5	22	51
Nonmarketable equity investments (1)	12	24	36	102
Total OTTI write-downs included in earnings (1)	$ 19	$ 29	$ 58	$ 153