Investment Securities (Investments, by type and length in continuous loss position) (Details) (USD $) In Millions, unless otherwise specified	Jun. 30, 2013	Dec. 31, 2012
Domestic Corporate Debt Securities [Member]
Investment [Line Items]
Estimated fair value, less than 12 months	$ 1,907	$ 434
Gross unrealized losses, less than 12 months	(119)	(7)
Estimated fair value, 12 months or more	365	813
Gross unrealized losses, less than 12 months	(63)	(295)
US States and Political Subdivisions Debt Securities [Member]
Investment [Line Items]
Estimated fair value, less than 12 months	962	146
Gross unrealized losses, less than 12 months	(66)	(2)
Estimated fair value, 12 months or more	295	326
Gross unrealized losses, less than 12 months	(109)	(111)
Residential Mortgage Backed Securities [Member]
Investment [Line Items]
Estimated fair value, less than 12 months	258	98
Gross unrealized losses, less than 12 months	(10)	(1)
Estimated fair value, 12 months or more	541	691
Gross unrealized losses, less than 12 months	(58)	(118)
Commercial Mortgage Backed Securities [Member]
Investment [Line Items]
Estimated fair value, less than 12 months	363	37
Gross unrealized losses, less than 12 months	(28)	0
Estimated fair value, 12 months or more	829	979
Gross unrealized losses, less than 12 months	(73)	(95)
Asset-backed Securities [Member]
Investment [Line Items]
Estimated fair value, less than 12 months	5,203	18
Gross unrealized losses, less than 12 months	(47)	(1)
Estimated fair value, 12 months or more	422	658
Gross unrealized losses, less than 12 months	(47)	(76)
Foreign Corporate Debt Securities [Member]
Investment [Line Items]
Estimated fair value, less than 12 months	81	167
Gross unrealized losses, less than 12 months	(1)	(8)
Estimated fair value, 12 months or more	621	602
Gross unrealized losses, less than 12 months	(98)	(118)
Foreign Government Debt Securities [Member]
Investment [Line Items]
Estimated fair value, less than 12 months	1,316	201
Gross unrealized losses, less than 12 months	(6)	(1)
Estimated fair value, 12 months or more	38	37
Gross unrealized losses, less than 12 months	(2)	(2)
US Treasury and Government [Member]
Investment [Line Items]
Estimated fair value, less than 12 months	262	0
Gross unrealized losses, less than 12 months	0	0
Estimated fair value, 12 months or more	0	0
Gross unrealized losses, less than 12 months	0	0
Retained Interest [Member]
Investment [Line Items]
Estimated fair value, less than 12 months	7	3
Gross unrealized losses, less than 12 months	0	0
Estimated fair value, 12 months or more	0	0
Gross unrealized losses, less than 12 months	0	0
Equity Securities [Member]
Investment [Line Items]
Estimated fair value, less than 12 months	35	26
Gross unrealized losses, less than 12 months	(17)	(3)
Estimated fair value, 12 months or more	0	0
Gross unrealized losses, less than 12 months	0	0
Total [Member]
Investment [Line Items]
Estimated fair value, less than 12 months	10,394	1,130
Gross unrealized losses, less than 12 months	(294)	(23)
Estimated fair value, 12 months or more	3,111	4,106
Gross unrealized losses, less than 12 months	$ (450)	$ (815)