Investment Securities (Investments, by type and length in continuous loss position) (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011
Domestic Corporate Debt Securities [Member]
Investment [Line Items]
Estimated fair value, less than 12 months	$ 434	$ 1,435
Gross unrealized losses, less than 12 months	(7)	(241)
Estimated fair value, 12 months or more	813	836
Gross unrealized losses, 12 months or more	(295)	(169)
US States and Political Subdivisions Debt Securities [Member]
Investment [Line Items]
Estimated fair value, less than 12 months	146	87
Gross unrealized losses, less than 12 months	(2)	(1)
Estimated fair value, 12 months or more	326	307
Gross unrealized losses, 12 months or more	(111)	(142)
Residential Mortgage Backed Securities [Member]
Investment [Line Items]
Estimated fair value, less than 12 months	98	219
Gross unrealized losses, less than 12 months	(1)	(9)
Estimated fair value, 12 months or more	691	825
Gross unrealized losses, 12 months or more	(118)	(277)
Commercial Mortgage Backed Securities [Member]
Investment [Line Items]
Estimated fair value, less than 12 months	37	244
Gross unrealized losses, less than 12 months	0	(23)
Estimated fair value, 12 months or more	979	1,320
Gross unrealized losses, 12 months or more	(95)	(224)
Asset-backed Securities [Member]
Investment [Line Items]
Estimated fair value, less than 12 months	18	100
Gross unrealized losses, less than 12 months	(1)	(7)
Estimated fair value, 12 months or more	658	850
Gross unrealized losses, 12 months or more	(76)	(157)
Foreign Corporate Debt Securities [Member]
Investment [Line Items]
Estimated fair value, less than 12 months	167	330
Gross unrealized losses, less than 12 months	(8)	(28)
Estimated fair value, 12 months or more	602	607
Gross unrealized losses, 12 months or more	(118)	(179)
Foreign Government Debt Securities [Member]
Investment [Line Items]
Estimated fair value, less than 12 months	201	906
Gross unrealized losses, less than 12 months	(1)	(5)
Estimated fair value, 12 months or more	37	203
Gross unrealized losses, 12 months or more	(2)	(81)
US Treasury and Government [Member]
Investment [Line Items]
Estimated fair value, less than 12 months	0	502
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
Retained Interest [Member]
Investment [Line Items]
Estimated fair value, less than 12 months	3	0
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	26	440
Gross unrealized losses, less than 12 months	(3)	(38)
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	1,130	4,263
Gross unrealized losses, less than 12 months	(23)	(352)
Estimated fair value, 12 months or more	4,106	4,948
Gross unrealized losses, 12 months or more	$ (815)	$ (1,229)