Outstanding Exposure - BIG Net Par Outstanding (Details) $ in Millions		Dec. 31, 2016 USD ($) risk		Dec. 31, 2015 USD ($) risk
Schedule of Insured Financial Obligations [Line Items]
Net Par Outstanding, Credit Derivative	[1]	$ 16,997		$ 25,594
Net Par Outstanding		$ 296,318	[2]	358,571	[3]
Number of Risks | risk		11,499
BIG [Member]
Schedule of Insured Financial Obligations [Line Items]
Net Par Outstanding, Financial Guaranty Insurance	[4]	$ 12,101		13,574
Net Par Outstanding, Credit Derivative		973		1,609
Net Par Outstanding		$ 13,074	[2]	$ 15,183	[3]
Number of Risks, Financial Guaranty Insurance | risk	[4],[5],[6]	392		419
Number of Risks, Credit Derivative | risk	[5]	25		32
Number of Risks | risk	[5]	417		451
BIG [Member] | BIG 1 [Member]
Schedule of Insured Financial Obligations [Line Items]
Net Par Outstanding, Financial Guaranty Insurance	[4]	$ 3,861		$ 7,019
Net Par Outstanding, Credit Derivative		634		1,004
Net Par Outstanding		$ 4,495		$ 8,023
Number of Risks, Financial Guaranty Insurance | risk	[4],[5]	165		202
Number of Risks, Credit Derivative | risk	[5]	10		12
Number of Risks | risk	[5]	175		214
BIG [Member] | BIG 2 [Member]
Schedule of Insured Financial Obligations [Line Items]
Net Par Outstanding, Financial Guaranty Insurance	[4]	$ 3,857		$ 3,655
Net Par Outstanding, Credit Derivative		202		474
Net Par Outstanding		$ 4,059		$ 4,129
Number of Risks, Financial Guaranty Insurance | risk	[4],[5]	79		85
Number of Risks, Credit Derivative | risk	[5]	6		8
Number of Risks | risk	[5]	85		93
BIG [Member] | BIG 3 [Member]
Schedule of Insured Financial Obligations [Line Items]
Net Par Outstanding, Financial Guaranty Insurance	[4]	$ 4,383		$ 2,900
Net Par Outstanding, Credit Derivative		137		131
Net Par Outstanding		$ 4,520		$ 3,031
Number of Risks, Financial Guaranty Insurance | risk	[4],[5]	148		132
Number of Risks, Credit Derivative | risk	[5]	9		12
Number of Risks | risk	[5]	157		144

[1] The December 31, 2016 total amount includes $1.7 billion net par outstanding of credit derivatives from CIFG Acquisition.

[2] The December 31, 2016 amounts include $2.9 billion of net par from the CIFG Acquisition.

[3] The December 31, 2015 amounts include $10.9 billion of net par from the Radian Asset Acquisition.

[4] Includes net par outstanding for VIEs.

[5] A risk represents the aggregate of the financial guaranty policies that share the same revenue source for purposes of making debt service payments.

[6] A risk represents the aggregate of the financial guaranty policies that share the same revenue source for purposes of making debt service payments. The ceded number of risks represents the number of risks for which the Company ceded a portion of its exposure.