Condensed Consolidated Statements of Cash Flows (unaudited) - USD ($) $ in Millions	6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017
Statement of Cash Flows [Abstract]
Net cash flows provided by (used in) operating activities	$ 444	$ 198
Fixed-maturity securities:
Purchases	(879)	(1,143)
Sales	592	778
Maturities	533	462
Net sales (purchases) of short-term investments	(304)	20
Net proceeds from paydowns on financial guaranty variable interest entities’ assets	60	81
Acquisition of MBIA UK Insurance Limited, net of cash acquired	0	95
Other	(16)	68
Net cash flows provided by (used in) investing activities	(14)	361
Financing activities
Dividends paid	(37)	(36)
Repurchases of common stock	(250)	(351)
Repurchases of common stock to pay withholding taxes	(13)	(12)
Net paydowns of financial guaranty variable interest entities’ liabilities	(61)	(86)
Paydown of long-term debt	(24)	(6)
Proceeds from option exercises	1	3
Net cash flows provided by (used in) financing activities	(384)	(488)
Effect of foreign exchange rate changes	(1)	3
Increase (decrease) in cash and restricted cash	45	74
Cash and restricted cash at beginning of period	144	127
Cash and restricted cash at end of period	189	201
Supplemental cash flow information
Income taxes	39	(7)
Interest	$ 57	$ 45