Loss Reserves (Details) (USD $)	3 Months Ended	6 Months Ended	12 Months Ended
	Sep. 30, 2012	Jun. 30, 2009	Dec. 31, 2012		Dec. 31, 2011		Dec. 31, 2010		Dec. 31, 2009
Loss Reserve [Roll Forward]
Reserve at beginning of period			$ 4,557,512,000		$ 5,884,171,000		$ 6,704,990,000
Less reinsurance recoverable			154,607,000		275,290,000		332,227,000
Net reserve at beginning of year			4,402,905,000	[1],[2]	5,608,881,000	[1],[2]	6,372,763,000	[1]
Adjustment to reserves			0	[3]	0	[3]	(92,000,000)	[3]
Adjusted beginning reserves			4,402,905,000		5,608,881,000		6,280,763,000
Losses and LAE incurred in respect of default notices received in [Abstract]
Current year			1,494,133,000		1,814,035,000		1,874,449,000
Prior years			573,120,000	[4]	(99,328,000)	[4]	(266,908,000)	[4]
Subtotal			2,067,253,000	[5]	1,714,707,000	[5]	1,607,541,000	[5]
Losses and LAE paid in respect of default notices received in [Abstract]
Current year			134,509,000		121,383,000		60,897,000
Prior years			2,389,985,000	[6]	2,838,069,000	[6]	2,256,206,000	[6]
Reinsurance terminations			(6,331,000)	[7]	(38,769,000)	[7]	(37,680,000)	[7]
Subtotal			2,518,163,000	[8]	2,920,683,000	[8]	2,279,423,000	[8]
Net reserve at end of period			3,951,995,000	[2]	4,402,905,000	[1],[2]	5,608,881,000	[1],[2]	6,372,763,000	[1]
Plus reinsurance recoverables			104,848,000		154,607,000		275,290,000		332,227,000
Reserve at end of period			4,056,843,000		4,557,512,000		5,884,171,000		6,704,990,000
Loss reserve reduction from rescission					700,000,000		1,300,000,000		2,100,000,000
Paid losses mitigated by rescission amount			300,000,000		600,000,000		1,000,000,000
Payment under the Freddie Mac settlement agreement			100,000,000
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Change in loss reserves			573,000,000		(99,000,000)		(267,000,000)
Historical average period for uncured default to develop into paid claim			12 months
Premium refund liability, expected claim payments			134,000,000		114,000,000
Primary Default Inventory [Roll Forward]
Default inventory at beginning of period			175,639		214,724		250,440
New Notices			133,232		169,305		205,069
Cures			(120,248)		(149,643)		(183,017)
Paids (including those charged to a deductible or captive)			(45,741)		(51,138)		(43,826)
Rescissions and denials			(3,037)		(7,609)		(13,942)
Default inventory at end of period			139,845		175,639		214,724		250,440
Number of rescindable loans affected by Company's decision to suspend rescissions for Countrywide			2,150
Total potential claim payments of rescindable loans affected by Company's decision to suspend rescissions for Countrywide			160,000,000
Number of rescindable loans affected by Company's decision to suspend rescissions for a specific customer			250
Total potential claim payments of rescindable loans affected by Company's decision to suspend rescissions for a specific customer			17,000,000
Number of rescindable loans affected by Company's decision to suspend rescissions for all other customers			240
Total potential claim payments of rescindable loans affected by Company's decision to suspend rescissions for all other customers			16,000,000
Pool insurance notice inventory [Abstract]
Pool insurance notice inventory (in number of loans)			8,594		32,971		43,329
Number of notices removed from pool notice inventory	15,600
Aging of the Primary Default Inventory [Abstract]
3 months or less			23,282		31,456		37,640
3 months or less (in hundredths)			17.00%		18.00%		18.00%
4 - 11 months			34,688		46,352		58,701
4 - 11 months (in hundredths)			25.00%		26.00%		27.00%
12 months or more			81,875		97,831		118,383
12 months or more (in hundredths)			58.00%		56.00%		55.00%
Total primary default inventory			139,845		175,639		214,724		250,440
Total primary default inventory (in hundredths)			100.00%		100.00%		100.00%
Primary claims received inventory included in ending default inventory			11,731	[9]	12,610	[9]	20,898	[9]
Primary claims received inventory included in ending default inventory (in hundredths)			8.00%	[9]	7.00%	[9]	10.00%	[9]
Number of payments delinquent [Abstract]
3 payments or less			34,245		42,804		51,003
3 payments or less (in hundredths)			24.00%		24.00%		24.00%
4 - 11 payments			34,458		47,864		65,797
4 - 11 payments (in hundredths)			25.00%		27.00%		31.00%
12 payments or more			71,142		84,971		97,924
12 payments or more (in hundredths)			51.00%		49.00%		45.00%
Total primary default inventory			139,845		175,639		214,724		250,440
Total primary default inventory (in hundredths)			100.00%		100.00%		100.00%
Claims resolved by rescissions [Abstract]
Mitigation of paid losses by rescission of policies			300,000,000		600,000,000		1,200,000,000		1,200,000,000
Percentage of claims received in a quarter resolved by rescission, lower range limit (in hundredths)			10.00%
Percentage of claims received in a quarter resolved by rescission, upper range limit (in hundredths)		28.00%
Estimated Rescission Reduction - Loss Reserve [Roll Forward]
Estimated rescission reduction - beginning reserve			700,000,000		1,300,000,000		2,100,000,000
Estimated rescission reduction - losses incurred			(200,000,000)	[10]	0	[10]	200,000,000	[10]
Rescission reduction - paid claims			300,000,000		600,000,000		1,200,000,000
Amounts that may have been applied to a deductible			0		0		(200,000,000)
Net rescission reduction - paid claims			300,000,000		600,000,000		1,000,000,000
Estimated rescission reduction - ending reserve			200,000,000		700,000,000		1,300,000,000		2,100,000,000
Number of settlement are probable			2
Mitigation of incurred losses by rescission of policies			0		0		200,000,000		2,500,000,000
Premium refund liability, expected future rescissions			18,000,000		58,000,000
Statute of limitations to bring legal proceedings disputing right to rescind coverage			3 years
Estimated benefit due to adjustment to loss reserves			100,000,000
Pool Policy Settlement [Member]
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Change in loss reserves			267,000,000	[11]	0	[11]	0	[11]
Estimated Probable Rescission Settlements [Member]
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Change in loss reserves			100,000,000	[11]	0	[11]	0	[11]
Increase (Decrease) in Estimated Claim Rate On primary Defaults [Member]
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Change in loss reserves			260,000,000		200,000,000		(432,000,000)
Percentage of prior year default inventory resolved (in hundredths)			55.00%		57.00%		55.00%
Decrease in Estimated Severity, Primary Defaults [Member]
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Change in loss reserves			(70,000,000)		(165,000,000)		0
Change In Estimates Related to Pool Reserves, LAE Reserves and Reinsurance [Member]
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Change in loss reserves			16,000,000	[12]	(134,000,000)	[12]	165,000,000	[12]
Increase (Decrease) Related To LAE and Pool Reserves [Member]
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Change in loss reserves					$ (114,000,000)		$ 185,000,000

[1] At December 31, 2011, 2010 and 2009 the estimated reduction in loss reserves related to rescissions approximated $0.7 billion, $1.3 billion and $2.1 billion, respectively.

[2] At December 31, 2012, 2011 and 2010 the estimated reduction in loss reserves related to rescissions approximated $0.2 billion, $0.7 billion and $1.3 billion, respectively.

[3] In periods prior to 2010 an estimate of premium to be refunded in conjunction with claim payments was included in Loss Reserves. In 2010, we separately stated portions of this liability in Other liabilities and Premium deficiency reserve on the consolidated balance sheet.

[4] A negative number for prior year losses incurred indicates a redundancy of prior year loss reserves, and a positive number for prior year losses incurred indicates a deficiency of prior year loss reserves. See table below regarding prior year loss development.

[5] Our estimated rescissions were reduced by approximately $0.2 billion in 2012 due to our probable settlement agreements (See Note 20 – "Litigation and Contingencies"), other rescissions had no significant impact on our losses incurred in 2012. Rescissions mitigated our incurred losses by an estimated $0.2 billion in 2010. Rescissions did not have a significant impact on incurred losses in 2011.

[6] In 2012, includes $0.1 billion payment under the Freddie Mac settlement agreement (See Note 20 – "Litigation and Contingencies").

[7] In a termination, the reinsurance agreement is cancelled, with no future premium ceded and funds for any incurred but unpaid losses transferred to us. The transferred funds result in an increase in our investment portfolio (including cash and cash equivalents) and a decrease in net losses paid (reduction to losses incurred). In addition, there is an offsetting decrease in the reinsurance recoverable (increase in losses incurred), and thus there is no net impact to losses incurred. (See Note 11 – "Reinsurance")

[8] Rescissions mitigated our paid losses by an estimated $0.3 billion, $0.6 billion and $1.0 billion in 2012, 2011 and 2010, respectively, which excludes amounts that may have been applied to a deductible.

[9] Our claims received inventory includes suspended rescissions as discussed in Note 20 – “Litigation and Contingencies”. In connection with the Countrywide proceedings, we have voluntarily suspended rescissions of coverage related to loans that we believe could be included in a potential resolution. As of December 31, 2012, coverage on approximately 2,150 loans, representing total potential claim payments of approximately $160 million, that we had determined was rescindable were affected by our decision to suspend such rescissions. Substantially all of these potential rescissions relate to claims received beginning in the first quarter of 2011 or later. As of December 31, 2012, coverage on approximately 250 loans, representing total potential claim payments of approximately $17 million, were affected by our decision to suspend rescissions for another customer for which we also consider settlement probable. In addition, as of December 31, 2012, approximately 240 rescissions, representing total potential claim payments of approximately $16 million, were affected by our decision to suspend rescissions for customers other than those for which we consider settlement probable, as defined in ASC 450-20.

[10] As discussed in Note 20 – “Litigation and Contingencies” we have made substantial progress in reaching an agreement with Countrywide to settle the dispute we have concerning rescissions. We have determined that a settlement with Countrywide is probable and under this probable settlement agreement, we estimate that our rescission benefit in loss reserves was reduced by approximately $0.2 billion. This adjustment to loss reserves was partially offset by an estimated benefit of approximately $0.1 billion under the terms of the settlement agreements we consider probable, as defined in ASC 450-20. As a result, in the fourth quarter of 2012, we increased our loss reserve estimates by approximately $0.1 billion to reflect potential settlements we consider probable.

[11] See Note 20 - "Litigation and Contingencies" for a discussion of our settlement with Freddie Mac and our probable settlements regarding rescissions.

[12] Includes approximately ($114) million related to LAE reserves in 2011 and approximately $185 million related to pool reserves in 2010.