Schedule I Condensed Statements of Cash Flows Schedule I Condensed Statements of Cash Flows (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Condensed Financial Statements, Captions [Line Items]
Cash flows from operating activities	$ 4,327	$ 3,220	$ 2,759
Cash flows from investing activities:
Purchases of available-for-sale securities	(110)	(123)	(106)
Proceeds from sale of available-for-sale securities	88	111	100
Other, net	(15)	(6)	35
Net cash flows from investing activities	(4,321)	(2,816)	(2,484)
Cash flows from financing activities:
Net proceeds from (repayments of) short-term debt	(6)	545	149
Net purchases of common stock	0	0	(56)
Other, net	(31)	(18)	(5)
Net cash flows from financing activities	477	(589)	(234)
Net change in cash and cash equivalents	490	(184)	41
Cash and cash equivalents at beginning of period	286	470	429
Cash and cash equivalents at end of period	776	286	470
Parent [Member]
Condensed Financial Statements, Captions [Line Items]
Cash flows from operating activities	1,019	792	(47)
Cash flows from investing activities:
Investments in subsidiaries	(1,164)	(157)	(214)
Purchases of available-for-sale securities	(46)	(38)	(15)
Proceeds from sale of available-for-sale securities	42	33	20
Notes receivable from affiliate, net	(15)	(217)	240
Other, net	(8)	(6)	0
Net cash flows from investing activities	(1,191)	(385)	31
Cash flows from financing activities:
Repayments of senior debt	(750)	0	0
Net proceeds from (repayments of) short-term debt	717	(176)	234
Notes payable to affiliate, net	220	106	120
Repayments of subordinated debt	(22)	(334)	(281)
Net purchases of common stock	0	0	(56)
Other, net	7	(8)	0
Net cash flows from financing activities	172	(412)	17
Net change in cash and cash equivalents	0	(5)	1
Cash and cash equivalents at beginning of period	13	18	17
Cash and cash equivalents at end of period	$ 13	$ 13	$ 18