Subsidiary Information - Condensed Consolidating Statement of Cash Flows (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Condensed Cash Flow Statements, Captions [Line Items]
Net cash flows provided by (used in) operating activities	$ (141)	$ (52)	$ 577
Fixed-maturity securities:
Purchases	(1,646)	(2,577)	(2,801)
Sales	1,365	2,107	1,251
Maturities	1,155	898	877
Sales (purchases) of short-term investments, net	17	897	158
Net proceeds from financial guaranty variable entities’ assets	629	400	408
Intercompany debt	0
Proceeds from stock redemption and return of capital from subsidiaries	0	0	0
Acquisition of Radian Asset, net of cash acquired	0	800	0
Acquisition of CIFG, net of cash acquired	435	0	0
Other	(9)	69	11
Net cash flows provided by (used in) investing activities	1,076	994	(96)
Cash flows from financing activities
Return of capital	0	0	0
Dividends paid	(69)	(72)	(76)
Repurchases of common stock	(306)	(555)	(590)
Share activity under option and incentive plans	10	(2)	1
Net paydowns of financial guaranty variable entities’ liabilities	(611)	(214)	(396)
Net proceeds from issuance of long-term debt	0	0	495
Payment of long-term debt	(2)	(4)	(19)
Intercompany debt	0
Net cash flows provided by (used in) financing activities	(978)	(847)	(585)
Effect of foreign exchange rate changes	(5)	(4)	(5)
Increase (decrease) in cash	(48)	91	(109)
Cash at beginning of period	166	75	184
Cash at end of period	118	166	75
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	390	513	758
Fixed-maturity securities:
Purchases	(4)	0	0
Sales	4	0	0
Maturities	0	0	0
Sales (purchases) of short-term investments, net	(26)	116	(93)
Net proceeds from financial guaranty variable entities’ assets	0	0	0
Intercompany debt	0
Proceeds from stock redemption and return of capital from subsidiaries	0	0	0
Acquisition of Radian Asset, net of cash acquired		0
Acquisition of CIFG, net of cash acquired	0
Other	0	0	0
Net cash flows provided by (used in) investing activities	(26)	116	(93)
Cash flows from financing activities
Return of capital	0	0	0
Dividends paid	(69)	(72)	(76)
Repurchases of common stock	(306)	(555)	(590)
Share activity under option and incentive plans	11	(2)	1
Net paydowns of financial guaranty variable entities’ liabilities	0	0	0
Net proceeds from issuance of long-term debt			0
Payment of long-term debt	0	0	0
Intercompany debt	0
Net cash flows provided by (used in) financing activities	(364)	(629)	(665)
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	533	408	223
Fixed-maturity securities:
Purchases	(143)	(72)	(540)
Sales	24	177	464
Maturities	30	9	6
Sales (purchases) of short-term investments, net	(237)	33	(15)
Net proceeds from financial guaranty variable entities’ assets	0	0	0
Intercompany debt	0
Proceeds from stock redemption and return of capital from subsidiaries	0	0	0
Acquisition of Radian Asset, net of cash acquired		0
Acquisition of CIFG, net of cash acquired	0
Other	7	(5)	0
Net cash flows provided by (used in) investing activities	(319)	142	(85)
Cash flows from financing activities
Return of capital	0	0	0
Dividends paid	(288)	(455)	(700)
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			495
Payment of long-term debt	0	0	0
Intercompany debt	(20)
Net cash flows provided by (used in) financing activities	(308)	(455)	(205)
Effect of foreign exchange rate changes	0	0	0
Increase (decrease) in cash	(94)	95	(67)
Cash at beginning of period	95	0	67
Cash at end of period	1	95	0
Reportable Legal Entities [Member] | AGMH (Issuer) [Member]
Condensed Cash Flow Statements, Captions [Line Items]
Net cash flows provided by (used in) operating activities	213	185	144
Fixed-maturity securities:
Purchases	(10)	(21)	(8)
Sales	12	30	10
Maturities	0	0	1
Sales (purchases) of short-term investments, net	(10)	19	(3)
Net proceeds from financial guaranty variable entities’ assets	0	0	0
Intercompany debt	0
Proceeds from stock redemption and return of capital from subsidiaries	300	25	50
Acquisition of Radian Asset, net of cash acquired		0
Acquisition of CIFG, net of cash acquired	0
Other	0	0	0
Net cash flows provided by (used in) investing activities	292	53	50
Cash flows from financing activities
Return of capital	0	0	0
Dividends paid	(513)	(234)	(190)
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
Payment of long-term debt	0	0	0
Intercompany debt	0
Net cash flows provided by (used in) financing activities	(513)	(234)	(190)
Effect of foreign exchange rate changes	0	0	0
Increase (decrease) in cash	(8)	4	4
Cash at beginning of period	8	4	0
Cash at end of period	0	8	4
Reportable Legal Entities [Member] | Other Entities [Member]
Condensed Cash Flow Statements, Captions [Line Items]
Net cash flows provided by (used in) operating activities	64	52	663
Fixed-maturity securities:
Purchases	(1,489)	(2,550)	(2,253)
Sales	1,325	1,900	777
Maturities	1,125	889	870
Sales (purchases) of short-term investments, net	290	729	269
Net proceeds from financial guaranty variable entities’ assets	629	400	408
Intercompany debt	20
Proceeds from stock redemption and return of capital from subsidiaries	4	0	0
Acquisition of Radian Asset, net of cash acquired		800
Acquisition of CIFG, net of cash acquired	442
Other	(9)	74	11
Net cash flows provided by (used in) investing activities	1,453	642	82
Cash flows from financing activities
Return of capital	(4)	(25)	(50)
Dividends paid	(540)	(455)	(321)
Repurchases of common stock	(300)	0	0
Share activity under option and incentive plans	(1)	0	0
Net paydowns of financial guaranty variable entities’ liabilities	(611)	(214)	(396)
Net proceeds from issuance of long-term debt			0
Payment of long-term debt	(2)	(4)	(19)
Intercompany debt	0
Net cash flows provided by (used in) financing activities	(1,458)	(698)	(786)
Effect of foreign exchange rate changes	(5)	(4)	(5)
Increase (decrease) in cash	54	(8)	(46)
Cash at beginning of period	63	71	117
Cash at end of period	117	63	71
Consolidating Adjustments [Member]
Condensed Cash Flow Statements, Captions [Line Items]
Net cash flows provided by (used in) operating activities	(1,341)	(1,210)	(1,211)
Fixed-maturity securities:
Purchases	0	66	0
Sales	0	0	0
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
Intercompany debt	(20)
Proceeds from stock redemption and return of capital from subsidiaries	(304)	(25)	(50)
Acquisition of Radian Asset, net of cash acquired		0
Acquisition of CIFG, net of cash acquired	(7)
Other	(7)	0	0
Net cash flows provided by (used in) investing activities	(324)	41	(50)
Cash flows from financing activities
Return of capital	4	25	50
Dividends paid	1,341	1,144	1,211
Repurchases of common stock	300	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
Payment of long-term debt	0	0	0
Intercompany debt	20
Net cash flows provided by (used in) financing activities	1,665	1,169	1,261
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