Subsidiary Information - Condensed Consolidating Statement of Cash Flows (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Condensed Cash Flow Statements, Captions [Line Items]
Net cash flows provided by (used in) operating activities	$ (52)	$ 577	$ 244
Fixed-maturity securities:
Purchases	(2,577)	(2,801)	(1,886)
Sales	2,107	1,251	1,029
Maturities	898	877	883
Sales (purchases) of short-term investments, net	897	158	(87)
Net proceeds from financial guaranty variable entities’ assets	400	408	663
Acquisition of Radian Asset	(800)	0	0
Intercompany debt	0	0	0
Investment in subsidiary	0	0	0
Other	69	11	79
Net cash flows provided by (used in) investing activities	994	(96)	681
Cash flows from financing activities
Return of capital	0	0	0
Capital contribution from parent	0	0	0
Dividends paid	(72)	(76)	(75)
Repurchases of common stock	(555)	(590)	(264)
Share activity under option and incentive plans	(2)	1	(1)
Net paydowns of financial guaranty variable entities’ liabilities	(214)	(396)	(511)
Net proceeds from issuance of long-term debt	0	495	0
Payment of long-term debt	(4)	(19)	(27)
Intercompany debt	0	0	0
Net cash flows provided by (used in) financing activities	(847)	(585)	(878)
Effect of foreign exchange rate changes	(4)	(5)	(1)
Increase (decrease) in cash	91	(109)	46
Cash at beginning of period	75	184	138
Cash at end of period	166	75	184
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	513	758	128
Fixed-maturity securities:
Purchases	0	0	0
Sales	0	0	176
Maturities	0	0	29
Sales (purchases) of short-term investments, net	116	(93)	7
Net proceeds from financial guaranty variable entities’ assets	0	0	0
Acquisition of Radian Asset	0
Intercompany debt	0	0	0
Investment in subsidiary	0	0	0
Other	0	0	0
Net cash flows provided by (used in) investing activities	116	(93)	212
Cash flows from financing activities
Return of capital	0	0	0
Capital contribution from parent	0	0	0
Dividends paid	(72)	(76)	(75)
Repurchases of common stock	(555)	(590)	(264)
Share activity under option and incentive plans	(2)	1	(1)
Net paydowns of financial guaranty variable entities’ liabilities	0	0	0
Net proceeds from issuance of long-term debt	0	0
Payment of long-term debt	0	0	0
Intercompany debt	0	0	0
Net cash flows provided by (used in) financing activities	(629)	(665)	(340)
Effect of foreign exchange rate changes	0	0	0
Increase (decrease) in cash	0	0	0
Cash at beginning of period	0	0	0
Cash at end of period	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	408	223	178
Fixed-maturity securities:
Purchases	(72)	(540)	(93)
Sales	177	464	1
Maturities	9	6	3
Sales (purchases) of short-term investments, net	33	(15)	(28)
Net proceeds from financial guaranty variable entities’ assets	0	0	0
Acquisition of Radian Asset	0
Intercompany debt	0	0	0
Investment in subsidiary	0	0	0
Other	(5)	0	0
Net cash flows provided by (used in) investing activities	142	(85)	(117)
Cash flows from financing activities
Return of capital	0	0	0
Capital contribution from parent	0	0	0
Dividends paid	(455)	(700)	0
Repurchases of common stock	0	0	0
Share activity under option and incentive plans	0	0	0
Net paydowns of financial guaranty variable entities’ liabilities	0	0	0
Net proceeds from issuance of long-term debt	0	495
Payment of long-term debt	0	0	0
Intercompany debt	0	0	(7)
Net cash flows provided by (used in) financing activities	(455)	(205)	(7)
Effect of foreign exchange rate changes	0	0	0
Increase (decrease) in cash	95	(67)	54
Cash at beginning of period	0	67	13
Cash at end of period	95	0	67
Reportable Legal Entities [Member] | AGMH (Issuer) [Member]
Condensed Cash Flow Statements, Captions [Line Items]
Net cash flows provided by (used in) operating activities	185	144	133
Fixed-maturity securities:
Purchases	(21)	(8)	(26)
Sales	30	10	25
Maturities	0	1	2
Sales (purchases) of short-term investments, net	19	(3)	(15)
Net proceeds from financial guaranty variable entities’ assets	0	0	0
Acquisition of Radian Asset	0
Intercompany debt	0	0	0
Investment in subsidiary	25	50	49
Other	0	0	0
Net cash flows provided by (used in) investing activities	53	50	35
Cash flows from financing activities
Return of capital	0	0	0
Capital contribution from parent	0	0	0
Dividends paid	(234)	(190)	(168)
Repurchases of common stock	0	0	0
Share activity under option and incentive plans	0	0	0
Net paydowns of financial guaranty variable entities’ liabilities	0	0	0
Net proceeds from issuance of long-term debt	0	0
Payment of long-term debt	0	0	0
Intercompany debt	0	0	0
Net cash flows provided by (used in) financing activities	(234)	(190)	(168)
Effect of foreign exchange rate changes	0	0	0
Increase (decrease) in cash	4	4	0
Cash at beginning of period	4	0	0
Cash at end of period	8	4	0
Reportable Legal Entities [Member] | Other Entities [Member]
Condensed Cash Flow Statements, Captions [Line Items]
Net cash flows provided by (used in) operating activities	52	663	347
Fixed-maturity securities:
Purchases	(2,550)	(2,253)	(1,832)
Sales	1,900	777	892
Maturities	889	870	849
Sales (purchases) of short-term investments, net	729	269	(51)
Net proceeds from financial guaranty variable entities’ assets	400	408	663
Acquisition of Radian Asset	(800)
Intercompany debt	0	0	7
Investment in subsidiary	0	0	0
Other	74	11	79
Net cash flows provided by (used in) investing activities	642	82	607
Cash flows from financing activities
Return of capital	(25)	(50)	(50)
Capital contribution from parent	0	0	1
Dividends paid	(455)	(321)	(374)
Repurchases of common stock	0	0	0
Share activity under option and incentive plans	0	0	0
Net paydowns of financial guaranty variable entities’ liabilities	(214)	(396)	(511)
Net proceeds from issuance of long-term debt	0	0
Payment of long-term debt	(4)	(19)	(27)
Intercompany debt	0	0	0
Net cash flows provided by (used in) financing activities	(698)	(786)	(961)
Effect of foreign exchange rate changes	(4)	(5)	(1)
Increase (decrease) in cash	(8)	(46)	(8)
Cash at beginning of period	71	117	125
Cash at end of period	63	71	117
Consolidating Adjustments [Member]
Condensed Cash Flow Statements, Captions [Line Items]
Net cash flows provided by (used in) operating activities	(1,210)	(1,211)	(542)
Fixed-maturity securities:
Purchases	66	0	65
Sales	0	0	(65)
Maturities	0	0	0
Sales (purchases) of short-term investments, net	0	0	0
Net proceeds from financial guaranty variable entities’ assets	0	0	0
Acquisition of Radian Asset	0
Intercompany debt	0	0	(7)
Investment in subsidiary	(25)	(50)	(49)
Other	0	0	0
Net cash flows provided by (used in) investing activities	41	(50)	(56)
Cash flows from financing activities
Return of capital	25	50	50
Capital contribution from parent	0	0	(1)
Dividends paid	1,144	1,211	542
Repurchases of common stock	0	0	0
Share activity under option and incentive plans	0	0	0
Net paydowns of financial guaranty variable entities’ liabilities	0	0	0
Net proceeds from issuance of long-term debt	0	0
Payment of long-term debt	0	0	0
Intercompany debt	0	0	7
Net cash flows provided by (used in) financing activities	1,169	1,261	598
Effect of foreign exchange rate changes	0	0	0
Increase (decrease) in cash	0	0	0
Cash at beginning of period	0	0	0
Cash at end of period	$ 0	$ 0	$ 0