Condensed Consolidated Statements of Cash Flows (unaudited) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Statement of Cash Flows [Abstract]
Net cash flows provided by (used in) operating activities	$ 27	$ 102
Fixed-maturity securities:
Purchases	(411)	(517)
Sales	409	323
Maturities	225	265
Net sales (purchases) of short-term investments	(116)	12
Net proceeds from paydowns on financial guaranty variable interest entities’ assets	33	46
Acquisition of MBIA UK, net of cash acquired	0	95
Other	(14)	(13)
Net cash flows provided by (used in) investing activities	126	211
Financing activities
Dividends paid	(18)	(19)
Repurchases of common stock	(100)	(216)
Repurchases of common stock to pay withholding taxes	(12)	(12)
Net paydowns of financial guaranty variable interest entities’ liabilities	(33)	(48)
Paydown of long-term debt	(19)	(1)
Proceeds from option exercises	1	2
Net cash flows provided by (used in) financing activities	(181)	(294)
Effect of foreign exchange rate changes	1	2
Increase (decrease) in cash and restricted cash	(27)	21
Cash and restricted cash at beginning of period (see Note 10)	144	127
Cash and restricted cash at end of period (see Note 10)	117	148
Supplemental cash flow information
Income taxes	10	(5)
Interest	$ 21	$ 8