Consolidated Statements of Cash Flows (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2014
Statement of Cash Flows [Abstract]
Net cash flows provided by (used in) operating activities	$ 23	$ 101
Fixed-maturity securities:
Purchases	(448)	(517)
Sales	841	155
Maturities	155	148
Net sales (purchases) of short-term investments	420	184
Net proceeds from paydowns on financial guaranty variable interest entities’ assets	30	286
Other	3	19
Net cash flows provided by (used in) investing activities	1,001	275
Financing activities
Dividends paid	(19)	(20)
Repurchases of common stock	(152)	(35)
Share activity under option and incentive plans	(5)	0
Net paydowns of financial guaranty variable interest entities’ liabilities	(39)	(281)
Repayment of long-term debt	(1)	(6)
Other	4	0
Net cash flows provided by (used in) financing activities	(212)	(342)
Effect of foreign exchange rate changes	(2)	1
Increase (decrease) in cash	810	35
Cash at beginning of period	75	184
Cash at end of period	885	219
Supplemental cash flow information
Income taxes	17	37
Interest	$ 7	$ 8