Loss Reserves (Details) (USD $)	3 Months Ended				6 Months Ended				12 Months Ended
	Jun. 30, 2011		Jun. 30, 2010		Jun. 30, 2011		Jun. 30, 2010		Dec. 31, 2010		Dec. 31, 2009
Loss Reserve [Roll Forward]
Reserve at beginning of period					$ 5,884,171,000		$ 6,704,990,000		$ 6,704,990,000
Less reinsurance recoverables					275,290,000		332,227,000		332,227,000
Net reserve at beginning of year					5,608,881,000	[1]	6,372,763,000	[1]	6,372,763,000	[1]
Losses and LAE incurred in respect of default notices received in [Abstract]
Current year					855,253,000		894,282,000
Prior years					(85,270,000)	[2]	(119,694,000)	[2]
Subtotal					769,983,000	[3]	774,588,000	[3]
Losses and LAE paid in respect of default notices received in [Abstract]
Current year					8,330,000		2,250,000
Prior years					1,496,727,000		1,095,898,000
Reinsurance terminations					(2,925,000)	[4]	(184,000)	[4]
Subtotal					1,502,132,000	[5]	1,097,964,000	[5]
Net reserve at end of period	4,876,732,000	[6]	6,049,387,000	[6]	4,876,732,000	[6]	6,049,387,000	[6]	5,608,881,000	[1]	6,372,763,000	[1]
Plus reinsurance recoverables	206,170,000		339,542,000		206,170,000		339,542,000		275,290,000		332,227,000
Reserve at end of period	5,082,902,000		6,388,929,000		5,082,902,000		6,388,929,000		5,884,171,000		6,704,990,000
Losses incurred [Abstract]
Number of new default notices received, net of cures					1,696		5,074
Change in loss reserves					85,000,000		120,000,000
Losses paid [Abstract]
Historical average period for an uncured default to develop into a paid claim (in months)					12
Premium refund liability, expected claim payments	112,000,000				112,000,000				113,000,000
Premium refund liability, expected future rescissions	75,000,000				75,000,000				101,000,000
Pool insurance notice inventory [Abstract]
Pool insurance notice inventory (in number of loans)	36,552		42,872		36,552		42,872		43,329
Aging of the Primary Default Inventory [Abstract]
3 months or less	30,107		35,838		30,107		35,838		37,640
3 months or less (in hundredths)	16.00%		16.00%		16.00%		16.00%		18.00%
4 - 11 months	48,148		71,089		48,148		71,089		58,701
4 - 11 months (in hundredths)	26.00%		31.00%		26.00%		31.00%		27.00%
12 months or more	106,197		121,528		106,197		121,528		118,383
12 months or more (in hundredths)	58.00%		53.00%		58.00%		53.00%		55.00%
Total primary default inventory	184,452		228,455		184,452		228,455		214,724		250,440
Total primary default inventory (in hundredths)	100.00%		100.00%		100.00%		100.00%		100.00%
Loans in our default inventory in our claims received inventory	14,504		19,724		14,504		19,724		20,898
Loans in our default inventory in our claims received inventory (in hundredths)	8.00%		9.00%		8.00%		9.00%		10.00%
Number of payments delinquent [Abstract]
3 payments or less	40,968		49,308		40,968		49,308		51,003
3 payments or less (in hundredths)	22.00%		22.00%		22.00%		22.00%		24.00%
4 - 11 payments	51,523		80,224		51,523		80,224		65,797
4 - 11 payments (in hundredths)	28.00%		35.00%		28.00%		35.00%		31.00%
12 payments or more	91,961		98,923		91,961		98,923		97,924
12 payments or more (in hundredths)	50.00%		43.00%		50.00%		43.00%		45.00%
Total primary default inventory	184,452		228,455		184,452		228,455		214,724		250,440
Total primary default inventory (in hundredths)	100.00%		100.00%		100.00%		100.00%		100.00%
Estimated Rescission Reduction - Loss Reserve [Roll Forward]
Estimated rescission reduction - beginning reserve	1,100,000,000		2,400,000,000		1,300,000,000		2,100,000,000		2,100,000,000
Estimated rescission reduction - losses incurred	0		0		0		600,000,000
Rescission reduction - paid claims	200,000,000		200,000,000		400,000,000		600,000,000
Amounts that may have been applied to a deductible	0		(100,000,000)		0		(200,000,000)
Net rescission reduction - paid claims	200,000,000		100,000,000		400,000,000		400,000,000		1,200,000,000		1,200,000,000
Estimated rescission reduction - ending reserve	900,000,000		2,300,000,000		900,000,000		2,300,000,000		1,300,000,000		2,100,000,000
Primary Default Inventory [Roll Forward]
Default inventory at beginning of period	195,885		241,244		214,724		250,440		250,440
Plus: New Notices	39,972		48,181		83,167		101,574
Less: Cures	(35,832)		(47,290)		(81,471)		(96,500)
Less: Paids (including those charged to a deductible or captive)	(13,553)		(10,653)		(27,019)		(19,847)
Less: Rescissions and denials	(2,020)		(3,027)		(4,949)		(7,212)
Default inventory at end of period	184,452		228,455		184,452		228,455		214,724		250,440
Decrease in Estimated Loss Adjustment Expenses [Member]
Losses incurred [Abstract]
Change in loss reserves					80,000,000
Increase (Decrease) in Severity, Primary Defaults [Member]
Losses incurred [Abstract]
Change in loss reserves					(80,000,000)		150,000,000
Percentage of prior year default inventory resolved (in hundredths)					37.00%
Increase (Decrease) in Expected Claim Rate [Member]
Losses incurred [Abstract]
Change in loss reserves					65,000,000		(330,000,000)
Percentage of prior year default inventory resolved (in hundredths)							34.00%
Increase Related to Pool Reserves and Reinsurance [Member]
Losses incurred [Abstract]
Change in loss reserves					10,000,000
Increase (Decrease) in Severity, Pool Defaults [Member]
Losses incurred [Abstract]
Change in loss reserves							50,000,000
Decrease Related to LAE Reserves and Reinsurance [Member]
Losses incurred [Abstract]
Change in loss reserves							$ 10,000,000

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

[2] 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.

[3] Rescissions did not have a material impact on incurred losses in the six months ended June 30, 2011. Rescissions mitigated our incurred losses by an estimated $0.6 billion in the six months ended June 30, 2010.

[4] 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.

[5] Rescissions mitigated our paid losses by an estimated $0.4 billion in each of the six months ended June 30, 2011 and 2010, which excludes amounts that may have been applied to a deductible.

[6] At June 30, 2011 and 2010, the estimated reduction in loss reserves related to rescissions approximated $0.9 billion and $2.3 billion, respectively.