Consolidated Statements of Cash Flows (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012
Statement of Cash Flows [Abstract]
Net cash flows provided by (used in) operating activities	$ (14)	$ 75
Fixed maturity securities:
Purchases	(510)	(383)
Sales	183	189
Maturities	283	253
Net sales (purchases) of short-term investments	88	(143)
Net proceeds from paydowns on financial guaranty variable interest entities' assets	138	138
Other	55	53
Net cash flows provided by (used in) investing activities	237	107
Financing activities
Dividends paid	(19)	(16)
Repurchases of common stock	(39)	0
Share activity under option and incentive plans	(2)	(3)
Net paydowns of financial guaranty variable interest entities' liabilities	(167)	(193)
Repayment of long-term debt	(6)	(5)
Net cash flows provided by (used in) financing activities	(233)	(217)
Effect of exchange rate changes	(3)	2
Increase (decrease) in cash	(13)	(33)
Cash at beginning of period	138	215
Cash at end of period	125	182
Cash paid (received) during the period for:
Income taxes	32	2
Interest	$ 9	$ 12