Investment Securities (Investments, by type and length in continuous loss position) (Details) (USD $) In Millions, unless otherwise specified	Sep. 30, 2013	Dec. 31, 2012
Domestic Corporate Debt Securities [Member]
Investment [Line Items]
Estimated fair value, less than 12 months	$ 2,120	$ 434
Gross unrealized losses, less than 12 months	(134)	(7)
Estimated fair value, 12 months or more	416	813
Gross unrealized losses, 12 months or more	(75)	(295)
US States and Political Subdivisions Debt Securities [Member]
Investment [Line Items]
Estimated fair value, less than 12 months	996	146
Gross unrealized losses, less than 12 months	(84)	(2)
Estimated fair value, 12 months or more	313	326
Gross unrealized losses, 12 months or more	(105)	(111)
Residential Mortgage Backed Securities [Member]
Investment [Line Items]
Estimated fair value, less than 12 months	237	98
Gross unrealized losses, less than 12 months	(9)	(1)
Estimated fair value, 12 months or more	511	691
Gross unrealized losses, 12 months or more	(50)	(118)
Commercial Mortgage Backed Securities [Member]
Investment [Line Items]
Estimated fair value, less than 12 months	292	37
Gross unrealized losses, less than 12 months	(26)	0
Estimated fair value, 12 months or more	773	979
Gross unrealized losses, 12 months or more	(62)	(95)
Asset-backed Securities [Member]
Investment [Line Items]
Estimated fair value, less than 12 months	5,950	18
Gross unrealized losses, less than 12 months	(13)	(1)
Estimated fair value, 12 months or more	404	658
Gross unrealized losses, 12 months or more	(49)	(76)
Foreign Corporate Debt Securities [Member]
Investment [Line Items]
Estimated fair value, less than 12 months	140	167
Gross unrealized losses, less than 12 months	(1)	(8)
Estimated fair value, 12 months or more	495	602
Gross unrealized losses, 12 months or more	(95)	(118)
Foreign Government Debt Securities [Member]
Investment [Line Items]
Estimated fair value, less than 12 months	1,474	201
Gross unrealized losses, less than 12 months	(6)	(1)
Estimated fair value, 12 months or more	40	37
Gross unrealized losses, 12 months or more	(1)	(2)
US Treasury and Government [Member]
Investment [Line Items]
Estimated fair value, less than 12 months	444	0
Gross unrealized losses, less than 12 months	(40)	0
Estimated fair value, 12 months or more	0	0
Gross unrealized losses, 12 months or more	0	0
Retained Interest [Member]
Investment [Line Items]
Estimated fair value, less than 12 months	9	3
Gross unrealized losses, less than 12 months	0	0
Estimated fair value, 12 months or more	0	0
Gross unrealized losses, 12 months or more	0	0
Equity Securities [Member]
Investment [Line Items]
Estimated fair value, less than 12 months	16	26
Gross unrealized losses, less than 12 months	(3)	(3)
Estimated fair value, 12 months or more	0	0
Gross unrealized losses, 12 months or more	0	0
Total [Member]
Investment [Line Items]
Estimated fair value, less than 12 months	11,678	1,130
Gross unrealized losses, less than 12 months	(316)	(23)
Estimated fair value, 12 months or more	2,952	4,106
Gross unrealized losses, 12 months or more	$ (437)	$ (815)