Consolidated Balance Sheets (USD $) In Millions, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012
Assets
Cash and cash equivalents	$ 934	$ 990
Deferred income taxes, net	1,100
Total assets	21,592	21,724
Liabilities:
Total liabilities	18,283	18,530
Commitments and contingencies (See Note 13)
Equity:
Preferred stock, par value $1 per share; authorized shares-10,000,000; issued and outstanding-none
Common stock, par value $1 per share; authorized shares-400,000,000; issued shares-277,793,696 and 277,405,039	278	277
Additional paid-in capital	3,107	3,076
Retained earnings	2,203	2,039
Accumulated other comprehensive income (loss), net of tax of $18 and $21	9	56
Treasury stock, at cost-84,836,010 and 81,733,530 shares	(2,309)	(2,275)
Total shareholders' equity of MBIA Inc.	3,288	3,173
Preferred stock of subsidiary and noncontrolling interest	21	21
Total equity	3,309	3,194
Total liabilities and equity	21,592	21,724
Non Variable Interest Entities [Member]
Assets
Fixed-maturity securities held as available-for-sale, at fair value	4,215	4,485
Fixed-maturity securities at fair value	243	244
Investments pledged as collateral, at fair value (amortized cost $374 and $489)	333	443
Short-term investments held as available-for-sale, at fair value (amortized cost $859 and $662)	866	669
Other investments (includes investments at fair value of $13 and $12)	22	21
Total investments	5,679	5,862
Cash and cash equivalents	862	814
Premiums receivable	1,161	1,228
Deferred acquisition costs	290	302
Insurance loss recoverable	3,877	3,648
Property and equipment, at cost (less accumulated depreciation of $144 and $146)	68	69
Deferred income taxes, net	1,146	1,199
Other assets	238	268
Liabilities:
Unearned premium revenue	2,774	2,938
Loss and Loss Adjustment Expense Reserves	785	853
Investment agreements	915	944
Medium-term notes (includes financial instruments carried at fair value of $181 and $165)	1,577	1,598
Long-term debt	1,661	1,662
Derivative liabilities	3,006	2,934
Other liabilities	377	315
Variable Interest Entity [Member]
Assets
Cash	72	176
Investments held-to-maturity, at amortized cost (fair value $2,759 and $2,674)	2,826	2,829
Fixed-maturity securities held as available-for-sale, at fair value	623	625
Fixed-maturity securities at fair value	1,753	1,735
Loans receivable at fair value	1,819	1,881
Loan repurchase commitments	1,176	1,086
Other assets	2	2
Total assets	8,300	8,300
Liabilities:
Variable interest entity notes (includes financial instruments carried at fair value of $3,578 and $3,659)	7,039	7,124
Derivative liabilities	149	162
Total liabilities	$ 7,200	$ 7,300