Consolidated Statements of Cash Flows (unaudited) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016
Statement of Cash Flows [Abstract]
Net cash flows provided by (used in) operating activities	$ 354	$ (189)
Fixed-maturity securities:
Purchases	(1,615)	(1,028)
Sales	1,128	877
Maturities	689	861
Net sales (purchases) of short-term investments	(240)	80
Net proceeds from paydowns on financial guaranty variable interest entities’ assets	117	590
Acquisition of MBIA UK, net of cash acquired (see Note 2)	95	0
Acquisition of CIFG, net of cash acquired	0	(435)
Other	58	(12)
Net cash flows provided by (used in) investing activities	232	933
Financing activities
Dividends paid	(53)	(52)
Repurchases of common stock	(431)	(190)
Repurchases of common stock to pay withholding taxes	(13)	(2)
Net paydowns of financial guaranty variable interest entities’ liabilities	(124)	(567)
Repayment/ extinguishment of long-term debt	(29)	(2)
Proceeds from option exercises	5	6
Net cash flows provided by (used in) financing activities	(645)	(807)
Effect of foreign exchange rate changes	4	(4)
Increase (decrease) in cash and restricted cash	(55)	(67)
Cash and restricted cash at beginning of period (see Note 10)	127	166
Cash and restricted cash at end of period (see Note 10)	72	99
Supplemental cash flow information
Income taxes	3	2
Interest	$ 53	$ 55