Fair Value Measurement - Fair Value Level 3 Rollforward Recurring Basis (Details) - USD ($) $ in Millions		3 Months Ended			6 Months Ended
		Jun. 30, 2016	Jun. 30, 2015		Jun. 30, 2016	Jun. 30, 2015
Total Pretax Realized And Unrealized Gains (Losses) Recorded As Assets [Abstract]
Net Income (loss)	[1]	$ 0			$ 0
Other comprehensive income (loss)	[1]	0			0
Purchases		0			0
Settlements		0			(60)
FG VIE Consolidations		0			0
FG VIE deconsolidations		0			0
Fair value at end of period		0			0
Change in unrealized gains/(losses) related to financial instruments held		0			0
Short-term Investments [Member]
Fair Value Level 3 Rollforward
Fair value at beginning of period		0			60
FG VIEs' assets, at fair value [Member]
Fair Value Level 3 Rollforward
Fair value at beginning of period		1,191	$ 1,495		1,261	$ 1,398
Radian Asset Acquisition			122			122
Total Pretax Realized And Unrealized Gains (Losses) Recorded As Assets [Abstract]
Net Income (loss)	[1],[2]	113	19		109	42
Other comprehensive income (loss)	[1]	0	0		0	0
Purchases		0	0		0	0
Settlements		(490)	(40)		(556)	(70)
FG VIE Consolidations		0	0		0	104
FG VIE deconsolidations		0	0		0	0
Fair value at end of period		814	1,596		814	1,596
Change in unrealized gains/(losses) related to financial instruments held		11	31		15	65
Other Assets and Other Invested Assets [Member]
Fair Value Level 3 Rollforward
Fair value at beginning of period	[3]	49	40		65	37
Radian Asset Acquisition	[3]		2			2
Total Pretax Realized And Unrealized Gains (Losses) Recorded As Assets [Abstract]
Net Income (loss)	[1],[3],[4]	(11)	23		(27)	25
Other comprehensive income (loss)	[1],[3]	0	(1)		0	0
Purchases	[3]	0	0		0	0
Settlements	[3]	0	0		0	0
FG VIE Consolidations	[3]	0	0		0	0
FG VIE deconsolidations	[3]	0	0		0	0
Fair value at end of period	[3]	38	64		38	64
Change in unrealized gains/(losses) related to financial instruments held	[3]	(11)	22		(27)	25
Obligations of state and political subdivisions [Member] | Fixed Maturities [Member]
Fair Value Level 3 Rollforward
Fair value at beginning of period		7	8		8	38
Radian Asset Acquisition			0			0
Total Pretax Realized And Unrealized Gains (Losses) Recorded As Assets [Abstract]
Net Income (loss)	[1],[5]	0	0		0	3
Other comprehensive income (loss)	[1]	1	(1)		1	(3)
Purchases		33	0		33	0
Settlements		0	0	[6]	(1)	(31)	[6]
FG VIE Consolidations		0	0		0	0
FG VIE deconsolidations		0	0		0	0
Fair value at end of period		41	7		41	7
Change in unrealized gains/(losses) related to financial instruments held		1	0		1	0
Corporate securities [Member] | Fixed Maturities [Member]
Fair Value Level 3 Rollforward
Fair value at beginning of period		74	79		71	79
Radian Asset Acquisition			0			0
Total Pretax Realized And Unrealized Gains (Losses) Recorded As Assets [Abstract]
Net Income (loss)	[1],[5]	2	(3)		4	(1)
Other comprehensive income (loss)	[1]	(18)	1		(17)	(1)
Purchases		0	0		0	0
Settlements		0	0		0	0
FG VIE Consolidations		0	0		0	0
FG VIE deconsolidations		0	0		0	0
Fair value at end of period		58	77		58	77
Change in unrealized gains/(losses) related to financial instruments held		(18)	1		(17)	(1)
RMBS [Member] | Fixed Maturities [Member]
Fair Value Level 3 Rollforward
Fair value at beginning of period		360	383		348	425
Radian Asset Acquisition			4			4
Total Pretax Realized And Unrealized Gains (Losses) Recorded As Assets [Abstract]
Net Income (loss)	[1],[5]	4	8		2	17
Other comprehensive income (loss)	[1]	3	(9)		(2)	(4)
Purchases		6	1		40	10
Settlements		(24)	(51)		(39)	(116)
FG VIE Consolidations		0	(1)		0	(1)
FG VIE deconsolidations		0	0		0	0
Fair value at end of period		349	335		349	335
Change in unrealized gains/(losses) related to financial instruments held		2	(7)		(3)	(1)
Asset-backed Securities [Member] | Fixed Maturities [Member]
Fair Value Level 3 Rollforward
Fair value at beginning of period		639	226		657	228
Radian Asset Acquisition			0			0
Total Pretax Realized And Unrealized Gains (Losses) Recorded As Assets [Abstract]
Net Income (loss)	[1],[5]	10	3		11	1
Other comprehensive income (loss)	[1]	(5)	8		(10)	9
Purchases		0	0		0	0
Settlements		(80)	(1)		(94)	(2)
FG VIE Consolidations		0	0		0	0
FG VIE deconsolidations		0	0		0	0
Fair value at end of period		564	236		564	236
Change in unrealized gains/(losses) related to financial instruments held		(4)	8		(10)	9
FG VIEs' liabilities with recourse, at fair value [Member]
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair value at beginning of period		(1,165)	(1,278)		(1,225)	(1,277)
Radian Asset Acquisition			(114)			(114)
Total Pretax Realized And Unrealized Gains (Losses) Recorded As Liabilities [Abstract]
Net income (loss)	[1],[2]	(112)	(5)		(91)	88
Other comprehensive income (loss)	[1]	0	0		0	0
Purchases		0	0		0	0
Settlements		487	36		526	73
FG VIE consolidations		0	0		0	(131)
FG VIE deconsolidations		0	0		0	0
Fair value at end of period		(790)	(1,361)		(790)	(1,361)
Change in unrealized gains/(losses) related to financial instruments held		(2)	(6)		19	(12)
Financial Guaranty Variable Interest Liabilities without Recourse [Member]
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair value at beginning of period		(119)	(145)		(124)	(142)
Radian Asset Acquisition			(4)			(4)
Total Pretax Realized And Unrealized Gains (Losses) Recorded As Liabilities [Abstract]
Net income (loss)	[1],[2]	2	(25)		4	(30)
Other comprehensive income (loss)	[1]	0	0		0	0
Purchases		0	0		0	0
Settlements		2	3		5	5
FG VIE consolidations		0	0		0	0
FG VIE deconsolidations		0	0		0	0
Fair value at end of period		(115)	(171)		(115)	(171)
Change in unrealized gains/(losses) related to financial instruments held		2	(14)		3	(19)
Credit Risk Contract [Member]
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Roll Forward]
Fair value at start of period	[7]	(434)	(782)		(365)	(895)
Radian Asset Acquisition	[7]		(215)			(215)
Total Pretax Realized And Unrealized Gains (Losses) Recorded As Net Derivative Asset (Liability) [Abstract]
Net income (loss)	[1],[7],[8]	63	90		3	214
Other comprehensive income (loss)	[1],[7]	0	0		0	0
Purchases	[7]	0	0		0	0
Settlements	[7]	(25)	(19)		(34)	(30)
FG VIE consolidations	[7]	0	0		0	0
FG VIE deconsolidations	[7]	0	0		0	0
Fair value at end of period	[7]	(396)	(926)		(396)	(926)
Change in unrealized gains/(losses) related to financial instruments held	[7]	$ (20)	$ 82		$ (99)	$ 186

[1] Realized and unrealized gains (losses) from changes in values of Level 3 financial instruments represent gains (losses) from changes in values of those financial instruments only for the periods in which the instruments were classified as Level 3.

[2] Included in fair value gains (losses) on FG VIEs.

[3] Includes CCS and other invested assets.

[4] Recorded in fair value gains (losses) on CCS, net investment income and other income.

[5] Included in net realized investment gains (losses) and net investment income.

[6] Primarily non-cash transaction.

[7] Represents net position of credit derivatives. The consolidated balance sheet presents gross assets and liabilities based on net counterparty exposure.

[8] Reported in net change in fair value of credit derivatives.