Consolidated Statements of Cash Flows (unaudited) - USD ($) $ in Millions	6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016
Statement of Cash Flows [Abstract]
Net cash flows provided by (used in) operating activities	$ 198	$ (47)
Fixed-maturity securities:
Purchases	(1,143)	(510)
Sales	778	739
Maturities	462	645
Net sales (purchases) of short-term investments	20	(190)
Net proceeds from paydowns on financial guaranty variable interest entities’ assets	81	556
Acquisition of MBIA UK, net of cash acquired (see Note 2)	95	0
Other	68	(12)
Net cash flows provided by (used in) investing activities	361	1,228
Financing activities
Dividends paid	(36)	(35)
Repurchases of common stock	(351)	(135)
Repurchases of common stock to pay withholding taxes	(12)	(2)
Net paydowns of financial guaranty variable interest entities’ liabilities	(86)	(531)
Repayment/ extinguishment of long-term debt	(6)	(1)
Proceeds from option exercises	3	1
Net cash flows provided by (used in) financing activities	(488)	(703)
Effect of foreign exchange rate changes	3	(3)
Increase (decrease) in cash and restricted cash	74	475
Cash and restricted cash at beginning of period (see Note 10)	127	166
Cash and restricted cash at end of period (see Note 10)	201	641
Supplemental cash flow information
Income taxes	(7)	1
Interest	$ 45	$ 48