Loss Reserves (Details) (USD $)	3 Months Ended					12 Months Ended						36 Months Ended
	Mar. 31, 2013 Loan		Sep. 30, 2012 Notice	Mar. 31, 2012 Loan		Dec. 31, 2012 Loan		Dec. 31, 2011 Loan		Dec. 31, 2010	Dec. 31, 2009	Dec. 31, 2011 Loan
Loss Reserve [Roll Forward]
Net reserve at beginning of period	$ 4,056,843,000			$ 4,557,512,000		$ 4,557,512,000
Less reinsurance recoverable	104,848,000			154,607,000		154,607,000
Net reserve at end of period	3,752,169,000	[1]		4,066,881,000	[1]	3,951,995,000	[2]	4,402,905,000	[2]			4,402,905,000	[2]
Losses and LAE incurred in respect of default notices related to:
Current year	268,793,000			280,565,000
Prior years	(2,585,000)	[3]		56,523,000	[3]
Subtotal	266,208,000	[4]		337,088,000	[4]
Losses and LAE paid in respect of default notices related to:
Current year	246,000			280,000
Prior years	468,933,000			673,257,000
Reinsurance terminations	(3,145,000)	[5]		(425,000)	[5]
Subtotal	466,034,000	[6]		673,112,000	[6]
Net reserve at end of period	3,752,169,000	[1]		4,066,881,000	[1]	3,951,995,000	[2]	4,402,905,000	[2]			4,402,905,000	[2]
Plus reinsurance recoverables	96,179,000			142,289,000		104,848,000		154,607,000				154,607,000
Reserve at end of period	3,848,348,000			4,209,170,000		4,056,843,000		4,557,512,000				4,557,512,000
Loss reserve reduction from rescission	200,000,000			600,000,000		200,000,000		700,000,000				700,000,000
Paid losses mitigated by rescission amount	35,000,000			100,000,000
Causes of Increase (Decrease) in Liability for Unpaid Claims and Claims Adjustment Expense [Line Items]
Change in loss reserves	(3,000,000)	[7]		56,000,000	[7]
Historical average period for uncured default to develop into paid claim	12 months
Premium refund liability, expected claim payments	136,000,000					134,000,000
Primary Default Inventory [Roll Forward]
Default inventory at beginning of period	139,845			175,639		175,639
New Notices	27,864			34,781
Cures	(31,122)			(37,144)
Paids (including those charged to a deductible or captive)	(9,445)			(11,909)
Rescissions and denials	(532)			(894)
Default inventory at end of period	126,610			160,473		139,845		175,639				175,639
Number of rescindable loans affected by Company's decision to suspend rescissions for Countrywide	2,300
Total potential claim payments of rescindable loans affected by Company's decision to suspend rescissions for Countrywide	170,000,000
Number of rescindable loans affected by Company's decision to suspend rescissions for a specific customer	300
Total potential claim payments of rescindable loans affected by Company's decision to suspend rescissions for a specific customer	20,000,000
Number of rescindable loans affected by Company's decision to suspend rescissions for all other customers	265
Total potential claim payments of rescindable loans affected by Company's decision to suspend rescissions for all other customers	19,000,000
Pool insurance notice inventory [Abstract]
Pool insurance notice inventory (in number of loans)	7,890			26,601		8,594
Number of notices removed from pool notice inventory			15,600
Aging of the Primary Default Inventory [Abstract]
3 months or less	17,973			22,516		23,282
3 months or less (in hundredths)	14.00%			14.00%		17.00%
4 - 11 months	32,662			45,552		34,688
4 - 11 months (in hundredths)	26.00%			28.00%		25.00%
12 months or more	75,975			92,405		81,875
12 months or more (in hundredths)	60.00%			58.00%		58.00%
Total primary default inventory	126,610			160,473		139,845		175,639				175,639
Total primary default inventory (in hundredths)	100.00%			100.00%		100.00%
Primary claims received inventory included in ending default inventory	10,924	[8]		12,758	[8]	11,731	[8]
Primary claims received inventory included in ending default inventory (in hundredths)	9.00%	[8]		8.00%	[8]	8.00%	[8]
Number of payments delinquent [Abstract]
3 payments or less	28,376			33,579		34,245
3 payments or less (in hundredths)	23.00%			21.00%		24.00%
4 - 11 payments	32,253			45,539		34,458
4 - 11 payments (in hundredths)	25.00%			28.00%		25.00%
12 payments or more	65,981			81,355		71,142
12 payments or more (in hundredths)	52.00%			51.00%		51.00%
Total primary default inventory	126,610			160,473		139,845		175,639				175,639
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	35,000,000					300,000,000						3,000,000,000
Percentage of claims received in a quarter resolved by rescission, lower range limit (in hundredths)	8.00%
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 - losses incurred	0					(200,000,000)		0		200,000,000	2,500,000,000
Estimated rescission reduction - ending reserve	200,000,000					200,000,000
Rescissions dispute period not ended (in hundredths)	40.00%
Premium refund liability, expected future rescissions	13,000,000					18,000,000
Statute of limitations to bring legal proceedings disputing right to rescind coverage	3 years
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	(15,000,000)	[7]		50,000,000	[7]
Percentage of prior year default inventory resolved (in hundredths)	23.00%			22.00%
Increase (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	20,000,000	[7]		0	[7]
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	$ (8,000,000)	[7]		$ 6,000,000	[7]

[1] At March 31, 2013 and 2012, the estimated reduction in loss reserves related to rescissions approximated $0.2 billion and $0.6 billion, respectively.

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

[3] 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.

[4] Rescissions did not have a significant impact on incurred losses in the three months ended March 31, 2013 or 2012.

[5] 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.

[6] Rescissions mitigated our paid losses by an estimated $35 million in the three months ended March 31, 2013 and by an estimated $0.1 billion in the three months ended March 31, 2012, which excludes amounts that may have been applied to a deductible.

[7] A negative number for prior year loss development indicates a redundancy of prior year loss reserves, and a positive number indicates a deficiency of prior year loss reserves.

[8] Our claims received inventory includes suspended rescission as discussed in Note 5 – "Litigation and Contingencies." In connection with the Countrywide proceedings, we have voluntarily suspended rescissions of coverage related to loans that we believed would be included in a potential resolution. As of March 31, 2013, coverage on approximately 2,300 loans, representing total potential claim payments of approximately $170 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 March 31, 2013, coverage on approximately 300 loans, representing total potential claim payments of approximately $20 million, were affected by our decision to suspend rescissions for another customer for which we also consider settlement probable. In addition, as of March 31, 2013, approximately 265 rescissions, representing total potential claim payments of approximately $19 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.