Investment Securities (Investment) (Details) - USD ($) $ in Millions	6 Months Ended	12 Months Ended
Jun. 30, 2015	Dec. 31, 2014
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	$ 35,646	$ 33,289
Gross unrealized gain	3,989	5,189
Gross unrealized losses	(280)	(158)
Estimated fair value	39,355	38,320
Investments securities	39,355	38,320
US Corporate
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	19,970	19,810
Gross unrealized gain	3,013	3,962
Gross unrealized losses	(147)	(69)
Estimated fair value	22,836	23,703
State and municipal
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	4,015	4,173
Gross unrealized gain	398	555
Gross unrealized losses	(90)	(53)
Estimated fair value	4,323	4,675
Residential Mortgage Backed Securities
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	1,077	1,544
Gross unrealized gain	88	153
Gross unrealized losses	(7)	(5)
Estimated fair value	1,158	1,692
Commercial mortgage backed
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	2,344	2,903
Gross unrealized gain	133	170
Gross unrealized losses	(16)	(10)
Estimated fair value	2,461	3,063
Asset-backed
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	112	304
Gross unrealized gain	1	8
Gross unrealized losses	(15)	(17)
Estimated fair value	98	295
Corporate non US
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	812	908
Gross unrealized gain	101	109
Gross unrealized losses	0	(1)
Estimated fair value	913	1,016
Government - non-U.S.
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	1,688	1,560
Gross unrealized gain	154	152
Gross unrealized losses	(4)	(2)
Estimated fair value	1,838	1,710
U.S. Government and federal agency
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	5,504	1,957
Gross unrealized gain	80	56
Gross unrealized losses	0	0
Estimated fair value	5,584	2,013
Available-for-sale Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	105	109
Gross unrealized gain	21	24
Gross unrealized losses	(1)	(1)
Estimated fair value	125	132
Trading Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	19	21
Gross unrealized gain	0	0
Gross unrealized losses	0	0
Estimated fair value	19	$ 21
Mortgage-backed Securities, Issued by Private Enterprises [Member]
Schedule of Available-for-sale Securities [Line Items]
Investments securities	26
Mortgage-backed Securities, Issued by US Government Sponsored Enterprises [Member]
Schedule of Available-for-sale Securities [Line Items]
Investments securities	$ 1,132

Amount of investment in debt and equity securities categorized neither as held-to-maturity nor trading.

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