Condensed Consolidated Statement of Shareholders' Equity (unaudited) - USD ($) $ in Millions	Total	Common Shares	Additional Paid-in Capital	Retained Earnings	Accumulated Other Comprehensive Income	Deferred Equity Compensation	Total Shareholders’ Equity Attributable to Assured Guaranty Ltd.	Nonredeemable Noncontrolling Interests
Beginning balance (in shares) at Dec. 31, 2018		103,672,592
Beginning balance at Dec. 31, 2018	$ 6,555	$ 1	$ 86	$ 6,374	$ 93	$ 1	$ 6,555	$ 0
Increase (Decrease) in Shareholders' Equity
Net income	265			265			265
Dividends	(56)			(56)			(56)
Common stock repurchases (in shares)		(7,828,412)
Common stock repurchases	(340)		(88)	(252)			(340)
Shared based compensation (in shares)		650,963
Share based compensation	2		2				2
Other comprehensive income	226				226		226
Ending balance (in shares) at Sep. 30, 2019		96,495,143
Ending balance at Sep. 30, 2019	6,652	$ 1	0	6,331	319	1	6,652	0
Beginning balance (in shares) at Jun. 30, 2019		99,801,012
Beginning balance at Jun. 30, 2019	6,722	$ 1	0	6,425	295	1	6,722	0
Increase (Decrease) in Shareholders' Equity
Net income	69			69			69
Dividends	(18)			(18)			(18)
Common stock repurchases (in shares)		(3,400,677)
Common stock repurchases	(150)		(5)	(145)			(150)
Shared based compensation (in shares)		94,808
Share based compensation	5		5				5
Other comprehensive income	24				24		24
Ending balance (in shares) at Sep. 30, 2019		96,495,143
Ending balance at Sep. 30, 2019	6,652	$ 1	$ 0	6,331	319	1	6,652	0
Beginning balance (in shares) at Dec. 31, 2019		93,274,987
Beginning balance at Dec. 31, 2019	6,645	$ 1		6,295	342	1	6,639	6
Increase (Decrease) in Shareholders' Equity
Net income	220			214			214	6
Dividends	(53)			(53)			(53)
Reallocation of ownership interests	10							10
Contributions	44							44
Common stock repurchases (in shares)		(11,443,155)
Common stock repurchases	(320)			(320)			(320)
Shared based compensation (in shares)		417,453
Share based compensation	7			7			7
Distributions	(19)							(19)
Other comprehensive income	62				62		62
Ending balance (in shares) at Sep. 30, 2020		82,249,285
Ending balance at Sep. 30, 2020	6,596	$ 1		6,143	404	1	6,549	47
Beginning balance (in shares) at Jun. 30, 2020		84,062,384
Beginning balance at Jun. 30, 2020	6,489	$ 1		6,109	333	1	6,444	45
Increase (Decrease) in Shareholders' Equity
Net income	88			86			86	2
Dividends	(17)			(17)			(17)
Reallocation of ownership interests	0							0
Contributions	3							3
Common stock repurchases (in shares)		(1,857,323)
Common stock repurchases	(40)			(40)			(40)
Shared based compensation (in shares)		44,224
Share based compensation	5			5			5
Distributions	(3)							(3)
Other comprehensive income	71				71		71
Ending balance (in shares) at Sep. 30, 2020		82,249,285
Ending balance at Sep. 30, 2020	$ 6,596	$ 1		$ 6,143	$ 404	$ 1	$ 6,549	$ 47