Investment Securities (Investment) (Details) - USD ($) $ in Millions		9 Months Ended	12 Months Ended
		Sep. 30, 2015	Dec. 31, 2014
Schedule of Available-for-sale Securities [Line Items]
Amortized cost		$ 33,032	$ 33,289
Gross unrealized gain		4,121	5,189
Gross unrealized losses		(285)	(158)
Estimated fair value		36,868	38,320
Investments	[1]	36,868	38,320
US Corporate
Schedule of Available-for-sale Securities [Line Items]
Amortized cost		19,975	19,810
Gross unrealized gain		3,102	3,962
Gross unrealized losses		(178)	(69)
Estimated fair value		22,899	23,703
State and municipal
Schedule of Available-for-sale Securities [Line Items]
Amortized cost		3,972	4,173
Gross unrealized gain		439	555
Gross unrealized losses		(71)	(53)
Estimated fair value		4,340	4,675
Residential Mortgage Backed Securities
Schedule of Available-for-sale Securities [Line Items]
Amortized cost		905	1,544
Gross unrealized gain		84	153
Gross unrealized losses		(5)	(5)
Estimated fair value		984	1,692
Commercial mortgage backed
Schedule of Available-for-sale Securities [Line Items]
Amortized cost		2,295	2,903
Gross unrealized gain		121	170
Gross unrealized losses		(12)	(10)
Estimated fair value		2,405	3,063
Asset-backed
Schedule of Available-for-sale Securities [Line Items]
Amortized cost		107	304
Gross unrealized gain		1	8
Gross unrealized losses		(10)	(17)
Estimated fair value		97	295
Corporate non US
Schedule of Available-for-sale Securities [Line Items]
Amortized cost		769	908
Gross unrealized gain		101	109
Gross unrealized losses		(3)	(1)
Estimated fair value		867	1,016
Government - non-U.S.
Schedule of Available-for-sale Securities [Line Items]
Amortized cost		1,094	1,560
Gross unrealized gain		158	152
Gross unrealized losses		(1)	(2)
Estimated fair value		1,252	1,710
U.S. Government and federal agency
Schedule of Available-for-sale Securities [Line Items]
Amortized cost		3,783	1,957
Gross unrealized gain		99	56
Gross unrealized losses		0	0
Estimated fair value		3,882	2,013
Available-for-sale Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized cost		113	109
Gross unrealized gain		16	24
Gross unrealized losses		(4)	(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		23
Mortgage-backed Securities, Issued by US Government Sponsored Enterprises [Member]
Schedule of Available-for-sale Securities [Line Items]
Investments		$ 961

[1] Amounts may not add due to rounding.