Employee Benefit Plans - Narrative (Details) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Employee benefit plans [Line Items]
Recognized contribution expense	$ 11,000,000	$ 10,000,000	$ 9,000,000
Stock Options [Member]
Employee benefit plans [Line Items]
Aggregate intrinsic value of awards outstanding	13,000,000
Weighted average remaining contractual term of awards outstanding (in years)	2 years 11 months
Aggregate intrinsic value of exercisable awards	12,000,000
Weighted average remaining contractual term of exercisable awards (in years)	2 years 8 months
Unrecognized compensation expense	1,000,000
Expected weighted-average remaining service period for recognition of unrecognized compensation cost (in years)	1 year 3 months 18 days
Expected volatility, inputs, average historical share price volatility and implied volatilities of certain at-the-money actively traded call options	7 years
Risk free interest rate, inputs, implied U.S. Treasury yield currently available, term	7 years
Total intrinsic value of awards exercised	3,000,000	7,500,000	100,000
Amount received from exercise of awards	4,300,000	2,600,000	44,000
Stock Options [Member] | Employee [Member]
Employee benefit plans [Line Items]
Vesting period of awards (in years)	3 years
Stock Options [Member] | Employee [Member] | Minimum [Member]
Employee benefit plans [Line Items]
Years from grant date until expiration	7 years
Stock Options [Member] | Employee [Member] | Maximum [Member]
Employee benefit plans [Line Items]
Years from grant date until expiration	10 years
Stock Options [Member] | Directors [Member}
Employee benefit plans [Line Items]
Vesting period of awards (in years)	1 year
Stock Options [Member] | Directors [Member} | Minimum [Member]
Employee benefit plans [Line Items]
Years from grant date until expiration	7 years
Stock Options [Member] | Directors [Member} | Maximum [Member]
Employee benefit plans [Line Items]
Years from grant date until expiration	10 years
Performance Stock Options [Member]
Employee benefit plans [Line Items]
Years from grant date until expiration	7 years
Aggregate intrinsic value of awards outstanding	2,000,000
Weighted average remaining contractual term of awards outstanding (in years)	4 years 5 months
Expected weighted-average remaining service period for recognition of unrecognized compensation cost (in years)	0 years 10 months 24 days
Expected volatility, inputs, average historical share price volatility and implied volatilities of certain at-the-money actively traded call options	7 years
Risk free interest rate, inputs, implied U.S. Treasury yield currently available, term	7 years
Unrecognized compensation expense	300,000
Restricted Stock Awards [Member]
Employee benefit plans [Line Items]
Expected weighted-average remaining service period for recognition of unrecognized compensation cost (in years)	0 years 4 months 24 days
Unrecognized compensation expense	400,000
Total fair value of awards vested	1,000,000	1,000,000	1,000,000
Restricted Stock Awards [Member] | Employee [Member]
Employee benefit plans [Line Items]
Vesting period of awards (in years)	4 years
Restricted Stock Awards [Member] | Directors [Member}
Employee benefit plans [Line Items]
Vesting period of awards (in years)	1 year
Restricted Stock Units [Member]
Employee benefit plans [Line Items]
Expected weighted-average remaining service period for recognition of unrecognized compensation cost (in years)	1 year 10 months 24 days
Unrecognized compensation expense	5,200,000
Total fair value of awards delivered	5,000,000	5,000,000	6,000,000
Performance Restricted Stock Units [Member]
Employee benefit plans [Line Items]
Expected weighted-average remaining service period for recognition of unrecognized compensation cost (in years)	1 year 10 months 24 days
Unrecognized compensation expense	3,700,000
Employee Stock Purchase Plan [Member] | Employee Stock [Member]
Employee benefit plans [Line Items]
Value of shares that can be purchased as a percentage of participant's compensation	10.00%
Value of shares that can be purchased	25,000
Capital shares reserved for future issuance	600,000
Purchase price of shares as a percentage of the fair market value of the stock	85.00%
Assured Guaranty Ltd. 2004 Long-Term Incentive Plan [Member]
Employee benefit plans [Line Items]
Maximum number of common shares that may be delivered	18,670,000
Assured Guaranty Ltd. 2004 Long-Term Incentive Plan [Member] | Stock Options [Member]
Employee benefit plans [Line Items]
Number of common shares available for grant	10,712,661
Share-based Compensation Award, Tranche One [Member]
Employee benefit plans [Line Items]
Vesting percentage			35.00%
Share-based Compensation Award, Tranche One [Member] | Performance Stock Options [Member]
Employee benefit plans [Line Items]
Vesting percentage	35.00%
Share-based Compensation Award, Tranche Two [Member] | Performance Stock Options [Member]
Employee benefit plans [Line Items]
Vesting percentage	50.00%
Share-based Compensation Award, Tranche Two [Member] | Performance Restricted Stock Units [Member]
Employee benefit plans [Line Items]
Vesting percentage			100.00%
Share-based Compensation Award, Tranche Three [Member] | Performance Stock Options [Member]
Employee benefit plans [Line Items]
Vesting percentage	100.00%
Share-based Compensation Award, Tranche Three [Member] | Performance Restricted Stock Units [Member]
Employee benefit plans [Line Items]
Vesting percentage			200.00%
United States [Member] | Pension Plan [Member]
Employee benefit plans [Line Items]
Core contribution made by the company as a percentage of participant's compensation	6.00%
Number of years of service to become fully vested	1 year
United States [Member] | 401 (k) Plan [Member] | Pension Plan [Member]
Employee benefit plans [Line Items]
Maximum amount that can be contributed by eligible participants	17,500
Percentage by which employer contribution matches up to 6% of participant's compensation	100.00%
Maximum percentage of participant's compensation eligible for employer contribution match	6.00%
Performance Retention Plan [Member]
Employee benefit plans [Line Items]
Defined contribution expenses	$ 15,000,000	$ 17,000,000	$ 13,000,000
Number of installments for award vesting	3
Percentage of awards allocated to a performance period that includes the year of the award and the next year	25.00%
Percentage of awards allocated to a performance period that includes the year of the award and the next two years	25.00%
Percentage of awards allocated to a performance period that includes the year of the award and the next three years	50.00%