Earnings Per Share (Details) (USD $) In Millions, except Per Share data, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013
Basic earnings per share ("EPS"):
Net income (loss) attributable to Assured Guaranty Ltd.	$ 159	$ 219	$ 201	$ 75
Less: Distributed and undistributed income (loss) available to nonvested shareholders	0	0	0	0
Distributed and undistributed income (loss) available to common shareholders of AGL and subsidiaries	159	219	201	75
Basic shares	178.4	187.8	180.3	190.8
Basic (per share)	$ 0.89	$ 1.17	$ 1.12	$ 0.39
Diluted EPS:
Distributed and undistributed income (loss) available to common shareholders of AGL and subsidiaries	159	219	201	75
Plus: Re-allocation of undistributed income (loss) available to nonvested shareholders of AGL and subsidiaries	0	0	0	0
Distributed and undistributed income (loss) available to common shareholders of AGL and subsidiaries	$ 159	$ 219	$ 201	$ 75
Basic shares	178.4	187.8	180.3	190.8
Effect of dilutive securities:
Options and restricted stock awards (in shares)	1.1	1.0	1.0	0.9
Diluted shares	179.5	188.8	181.3	191.7
Diluted (per share)	$ 0.89	$ 1.16	$ 1.11	$ 0.39
Potentially dilutive securities excluded from computation of EPS because of antidilutive effect (in shares)	1.5	2.0	1.5	3.6