Condensed Consolidated Statements of Cash Flows (unaudited) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017
Statement of Cash Flows [Abstract]
Net cash flows provided by (used in) operating activities	$ 352	$ 354
Fixed-maturity securities:
Purchases	(1,478)	(1,615)
Sales	908	1,128
Maturities	746	689
Net sales (purchases) of short-term investments	(91)	(240)
Net proceeds from paydowns on financial guaranty variable interest entities’ assets	90	117
Acquisition of MBIA UK Insurance Limited, net of cash acquired	0	95
Proceeds from maturity of other invested asset	0	85
Other	19	(27)
Net cash flows provided by (used in) investing activities	194	232
Financing activities
Dividends paid	(55)	(53)
Repurchases of common stock	(380)	(431)
Repurchases of common stock to pay withholding taxes	(13)	(13)
Net paydowns of financial guaranty variable interest entities’ liabilities	(90)	(124)
Paydown of long-term debt	(73)	(29)
Proceeds from option exercises	5	5
Net cash flows provided by (used in) financing activities	(606)	(645)
Effect of foreign exchange rate changes	(2)	4
Increase (decrease) in cash and restricted cash	(62)	(55)
Cash and restricted cash at beginning of period	144	127
Cash and restricted cash at end of period	82	72
Supplemental cash flow information
Income taxes	(5)	3
Interest on long-term debt	$ 66	$ 53