Financial Guaranty Insurance - Narrative (Details) - USD ($) $ in Millions	6 Months Ended			12 Months Ended
	Jun. 30, 2016		Jun. 30, 2015	Dec. 31, 2015
Guarantor Obligations [Line Items]
Net par amount outstanding	$ 329,864	[1]		$ 358,571	[2]
Guaranteed investment contract, aggregate accreted balance	1,700
Assets of GIC issuers, aggregate market value	$ 800
Variable Rate Demand Obligation [Member]
Guarantor Obligations [Line Items]
Rate basis for bank bond rate	prime rate
Bonds held by bank, minimum installment payment period	5 years
Minimum [Member]
Guarantor Obligations [Line Items]
Weighted average risk-free rates for U.S. dollar denominated financial guaranty insurance obligations	0.00%			0.00%
Minimum [Member] | Variable Rate Demand Obligation [Member]
Guarantor Obligations [Line Items]
Bank bond rate (as a percent)	2.00%
Threshold period of bonds held by bank for right of accelerated repayment (in days)	90 days
Maximum [Member]
Guarantor Obligations [Line Items]
Weighted average risk-free rates for U.S. dollar denominated financial guaranty insurance obligations	2.46%			3.25%
Maximum [Member] | Variable Rate Demand Obligation [Member]
Guarantor Obligations [Line Items]
Bank bond rate (as a percent)	3.00%
Bank bond capped rate (as a percent)	25.00%
Threshold period of bonds held by bank for right of accelerated repayment (in days)	180 days
Cash [Member] | Minimum [Member]
Guarantor Obligations [Line Items]
Collateralization as a percentage of GIC balance	100.00%
Asset-backed Securities [Member] | Maximum [Member]
Guarantor Obligations [Line Items]
Collateralization as a percentage of GIC balance	108.00%
Termination of Swap Obligation due to Rating Downgrade [Member] | Maximum [Member] | AGM [Member]
Guarantor Obligations [Line Items]
Increase in losses as a result of an adverse outcome, minimum	$ 193
Termination of Swap Obligation due to Further Rating Downgrade [Member] | Maximum [Member] | AGM [Member]
Guarantor Obligations [Line Items]
Increase in losses as a result of an adverse outcome, minimum	455
Variable Rate Demand Obligation [Member] | AGM and AGC [Member]
Guarantor Obligations [Line Items]
Net par amount outstanding	5,400
Internal Credit, BBB Minus Rating [Member] | Variable Rate Demand Obligation [Member] | AGM and AGC [Member]
Guarantor Obligations [Line Items]
Net par amount outstanding	$ 300
Foreign Currency Concentration Risk [Member] | Premiums Receivable [Member]
Guarantor Obligations [Line Items]
Percentage of installment premiums denominated in currencies other than the U.S. dollar	55.00%		50.00%	52.00%

[1] Excludes $1.4 billion of loss mitigation securities insured and held by the Company as of June 30, 2016, which are primarily BIG.

[2] Excludes $1.5 billion of loss mitigation securities insured and held by the Company as of December 31, 2015, which are primarily BIG.