Subsidiary Information - Condensed Consolidating Statement of Cash Flows (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016	Dec. 31, 2016	Dec. 31, 2015
Condensed Cash Flow Statements, Captions [Line Items]
Net cash flows provided by (used in) operating activities	$ 102	$ (90)
Fixed-maturity securities:
Purchases	(517)	(296)
Sales	323	162
Maturities	265	301
Net sales (purchases) of short-term investments	12	(63)
Net proceeds from financial guaranty variable entities’ assets	46	66
Investment in subsidiary	0	0
Payment to acquire business	95
Other	(13)	2
Net cash flows provided by (used in) investing activities	211	172
Cash flows from financing activities
Proceeds from Contributed Capital	0
Return of capital		0
Dividends paid	(19)	(18)
Repurchases of common stock	(216)	(75)
Repurchases of common stock to pay withholding taxes	(12)	(2)
Net paydowns of financial guaranty variable interest entities’ liabilities	(48)	(42)
Payment of long-term debt	(1)	0
Proceeds from options exercises	2	1
Net cash flows provided by (used in) financing activities	(294)	(136)
Effect of foreign exchange rate changes	2	0
Increase (decrease) in cash	21	(54)
Cash and Restricted Cash	148	112	$ 127	$ 166
Reportable Legal Entities [Member] | Assured Guaranty Ltd. (Parent) [Member]
Condensed Cash Flow Statements, Captions [Line Items]
Net cash flows provided by (used in) operating activities	220	166
Fixed-maturity securities:
Purchases	0	(4)
Sales	0	1
Maturities	0	0
Net sales (purchases) of short-term investments	25	(69)
Net proceeds from financial guaranty variable entities’ assets	0	0
Investment in subsidiary	0	0
Payment to acquire business	0
Other	0	0
Net cash flows provided by (used in) investing activities	25	(72)
Cash flows from financing activities
Proceeds from Contributed Capital	0
Return of capital		0
Dividends paid	(19)	(18)
Repurchases of common stock	(216)	(75)
Repurchases of common stock to pay withholding taxes	(12)	(2)
Net paydowns of financial guaranty variable interest entities’ liabilities	0	0
Payment of long-term debt	0	0
Proceeds from options exercises	2	1
Net cash flows provided by (used in) financing activities	(245)	(94)
Effect of foreign exchange rate changes	0	0
Increase (decrease) in cash	0	0
Cash and Restricted Cash	0	0	0	0
Reportable Legal Entities [Member] | AGUS (Issuer) [Member]
Condensed Cash Flow Statements, Captions [Line Items]
Net cash flows provided by (used in) operating activities	105	17
Fixed-maturity securities:
Purchases	0	(11)
Sales	0	0
Maturities	3	0
Net sales (purchases) of short-term investments	75	11
Net proceeds from financial guaranty variable entities’ assets	0	0
Investment in subsidiary	(3)	0
Payment to acquire business	0
Other	0	0
Net cash flows provided by (used in) investing activities	75	0
Cash flows from financing activities
Proceeds from Contributed Capital	0
Return of capital		0
Dividends paid	(175)	(80)
Repurchases of common stock	0	0
Repurchases of common stock to pay withholding taxes	0	0
Net paydowns of financial guaranty variable interest entities’ liabilities	0	0
Payment of long-term debt	0	0
Proceeds from options exercises	0	0
Net cash flows provided by (used in) financing activities	(175)	(80)
Effect of foreign exchange rate changes	0	0
Increase (decrease) in cash	5	(63)
Cash and Restricted Cash	6	32	1	95
Reportable Legal Entities [Member] | AGMH (Issuer) [Member]
Condensed Cash Flow Statements, Captions [Line Items]
Net cash flows provided by (used in) operating activities	72	88
Fixed-maturity securities:
Purchases	(5)	0
Sales	2	0
Maturities	0	0
Net sales (purchases) of short-term investments	5	0
Net proceeds from financial guaranty variable entities’ assets	0	0
Investment in subsidiary	0	0
Payment to acquire business	0
Other	0	0
Net cash flows provided by (used in) investing activities	2	0
Cash flows from financing activities
Proceeds from Contributed Capital	0
Return of capital		0
Dividends paid	(73)	(87)
Repurchases of common stock	0	0
Repurchases of common stock to pay withholding taxes	0	0
Net paydowns of financial guaranty variable interest entities’ liabilities	0	0
Payment of long-term debt	0	0
Proceeds from options exercises	0	0
Net cash flows provided by (used in) financing activities	(73)	(87)
Effect of foreign exchange rate changes	0	0
Increase (decrease) in cash	1	1
Cash and Restricted Cash	1	9	0	8
Reportable Legal Entities [Member] | Other Entities [Member]
Condensed Cash Flow Statements, Captions [Line Items]
Net cash flows provided by (used in) operating activities	105	(74)
Fixed-maturity securities:
Purchases	(512)	(281)
Sales	321	161
Maturities	262	301
Net sales (purchases) of short-term investments	(93)	(5)
Net proceeds from financial guaranty variable entities’ assets	46	66
Investment in subsidiary	0	0
Payment to acquire business	95
Other	(13)	2
Net cash flows provided by (used in) investing activities	106	244
Cash flows from financing activities
Proceeds from Contributed Capital	3
Return of capital		0
Dividends paid	(152)	(120)
Repurchases of common stock	0	0
Repurchases of common stock to pay withholding taxes	0	0
Net paydowns of financial guaranty variable interest entities’ liabilities	(48)	(42)
Payment of long-term debt	(1)	0
Proceeds from options exercises	0	0
Net cash flows provided by (used in) financing activities	(198)	(162)
Effect of foreign exchange rate changes	2	0
Increase (decrease) in cash	15	8
Cash and Restricted Cash	141	71	126	63
Consolidating Adjustments [Member]
Condensed Cash Flow Statements, Captions [Line Items]
Net cash flows provided by (used in) operating activities	(400)	(287)
Fixed-maturity securities:
Purchases	0	0
Sales	0	0
Maturities	0	0
Net sales (purchases) of short-term investments	0	0
Net proceeds from financial guaranty variable entities’ assets	0	0
Investment in subsidiary	3	0
Payment to acquire business	0
Other	0	0
Net cash flows provided by (used in) investing activities	3	0
Cash flows from financing activities
Proceeds from Contributed Capital	(3)
Return of capital		0
Dividends paid	400	287
Repurchases of common stock	0	0
Repurchases of common stock to pay withholding taxes	0	0
Net paydowns of financial guaranty variable interest entities’ liabilities	0	0
Payment of long-term debt	0	0
Proceeds from options exercises	0	0
Net cash flows provided by (used in) financing activities	397	287
Effect of foreign exchange rate changes	0	0
Increase (decrease) in cash	0	0
Cash and Restricted Cash	$ 0	$ 0	$ 0	$ 0