Loss And Loss Adjustment Expense Reserves (Schedule Of Financial Guarantees And Related Claim Liability) (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended		12 Months Ended
	Mar. 31, 2012		Dec. 31, 2011
Loss And Loss Adjustment Expense Reserves [Line Items]
Number of policies	304		296
Number of issues	195	[1]	191	[1]
Remaining weighted average contract period (in years)	8.6		8.8
Gross insured contractual payments outstanding, Principal	$ 16,739	[2]	$ 16,504	[2]
Gross insured contractual payments outstanding, Interest	9,114	[2]	8,984	[2]
Gross insured contractual payments outstanding, Total	25,853	[2]	25,488
Gross claim liability	1,782		1,812
Less: Gross potential recoveries	3,882		3,813
Less: Discount, net	184		177
Net claim liability (recoverable)	(2,284)		(2,178)
Unearned premium revenue	303		308
Caution List Low [Member]
Loss And Loss Adjustment Expense Reserves [Line Items]
Number of policies	54		54
Number of issues	31	[1]	32	[1]
Remaining weighted average contract period (in years)	8.6		8.2
Gross insured contractual payments outstanding, Principal	3,929	[2]	4,310	[2]
Gross insured contractual payments outstanding, Interest	2,752	[2]	2,653	[2]
Gross insured contractual payments outstanding, Total	6,681	[2]	6,963
Unearned premium revenue	149		155
Caution List Medium [Member]
Loss And Loss Adjustment Expense Reserves [Line Items]
Number of policies	33		28
Number of issues	20	[1]	18	[1]
Remaining weighted average contract period (in years)	4.4		5.6
Gross insured contractual payments outstanding, Principal	2,005	[2]	1,213	[2]
Gross insured contractual payments outstanding, Interest	452	[2]	351	[2]
Gross insured contractual payments outstanding, Total	2,457	[2]	1,564
Unearned premium revenue	21		16
Caution List High [Member]
Loss And Loss Adjustment Expense Reserves [Line Items]
Number of policies	13		14
Number of issues	12	[1]	11	[1]
Remaining weighted average contract period (in years)	6.6		6.0
Gross insured contractual payments outstanding, Principal	524	[2]	561	[2]
Gross insured contractual payments outstanding, Interest	148	[2]	144	[2]
Gross insured contractual payments outstanding, Total	672	[2]	705
Unearned premium revenue	4		3
Classified List [Member]
Loss And Loss Adjustment Expense Reserves [Line Items]
Number of policies	204		200
Number of issues	132	[1]	130	[1]
Remaining weighted average contract period (in years)	9.5		9.6
Gross insured contractual payments outstanding, Principal	10,281	[2]	10,420	[2]
Gross insured contractual payments outstanding, Interest	5,762	[2]	5,836	[2]
Gross insured contractual payments outstanding, Total	16,043	[2]	16,256
Gross claim liability	1,782		1,812
Less: Gross potential recoveries	3,882		3,813
Less: Discount, net	184		177
Net claim liability (recoverable)	(2,284)		(2,178)
Unearned premium revenue	$ 129		$ 134

[1] - An "issue" represents the aggregate of financial guarantee policies that share the same revenue source for purposes of making debt service payments.

[2] - Represents contractual principal and interest payments due by the issuer of the obligations insured by MBIA.