Subsidiary Information - Condensed Consolidating Statement of Cash Flows (Details) - USD ($) $ in Millions	6 Months Ended		12 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Dec. 31, 2015
Condensed Cash Flow Statements, Captions [Line Items]
Net cash flows provided by (used in) operating activities	$ (47)	$ 105
Fixed-maturity securities:
Purchases	(510)	(1,172)
Sales	739	1,381
Maturities	645	411
Net sales (purchases) of short-term investments	(190)	382
Net proceeds from financial guaranty variable entities’ assets	556	70
Investment in subsidiary	0	0
Acquisition of Radian Asset, net of cash acquired	0	(800)
Cash restricted for CIFG acquisition	(451)	0
Other	(12)	27
Net cash flows provided by (used in) investing activities	777	299
Cash flows from financing activities
Return of capital	0	0
Dividends paid	(35)	(37)
Repurchases of common stock	(135)	(285)
Share activity under option and incentive plans	(1)	(2)
Net paydowns of financial guaranty variable interest entities’ liabilities	(531)	(78)
Payment of long-term debt	(1)	(2)
Net cash flows provided by (used in) financing activities	(703)	(404)
Effect of foreign exchange rate changes	(3)	0
Increase (decrease) in cash	24	0
Cash at beginning of period	166	75	$ 75
Cash at end of period	190	75	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	202	343
Fixed-maturity securities:
Purchases	(4)	0
Sales	4	0
Maturities	0	0
Net sales (purchases) of short-term investments	(31)	(19)
Net proceeds from financial guaranty variable entities’ assets	0	0
Investment in subsidiary	0	0
Acquisition of Radian Asset, net of cash acquired		0
Cash restricted for CIFG acquisition	0
Other	0	0
Net cash flows provided by (used in) investing activities	(31)	(19)
Cash flows from financing activities
Return of capital	0	0
Dividends paid	(35)	(37)
Repurchases of common stock	(135)	(285)
Share activity under option and incentive plans	0	(2)
Net paydowns of financial guaranty variable interest entities’ liabilities	0	0
Payment of long-term debt	0	0
Net cash flows provided by (used in) financing activities	(170)	(324)
Effect of foreign exchange rate changes	0	0
Increase (decrease) in cash	1	0
Cash at beginning of period	0	0	0
Cash at end of period	1	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	31	138
Fixed-maturity securities:
Purchases	(32)	(67)
Sales	0	159
Maturities	21	6
Net sales (purchases) of short-term investments	(12)	39
Net proceeds from financial guaranty variable entities’ assets	0	0
Investment in subsidiary	0	0
Acquisition of Radian Asset, net of cash acquired		0
Cash restricted for CIFG acquisition	0
Other	0	0
Net cash flows provided by (used in) investing activities	(23)	137
Cash flows from financing activities
Return of capital	0	0
Dividends paid	(103)	(275)
Repurchases of common stock	0	0
Share activity under option and incentive plans	0	0
Net paydowns of financial guaranty variable interest entities’ liabilities	0	0
Payment of long-term debt	0	0
Net cash flows provided by (used in) financing activities	(103)	(275)
Effect of foreign exchange rate changes	0	0
Increase (decrease) in cash	(95)	0
Cash at beginning of period	95	0	0
Cash at end of period	0	0	95
Reportable Legal Entities [Member] | AGMH (Issuer) [Member]
Condensed Cash Flow Statements, Captions [Line Items]
Net cash flows provided by (used in) operating activities	101	83
Fixed-maturity securities:
Purchases	0	(6)
Sales	10	27
Maturities	0	0
Net sales (purchases) of short-term investments	(11)	(1)
Net proceeds from financial guaranty variable entities’ assets	0	0
Investment in subsidiary	0	25
Acquisition of Radian Asset, net of cash acquired		0
Cash restricted for CIFG acquisition	0
Other	0	0
Net cash flows provided by (used in) investing activities	(1)	45
Cash flows from financing activities
Return of capital	0	0
Dividends paid	(103)	(128)
Repurchases of common stock	0	0
Share activity under option and incentive plans	0	0
Net paydowns of financial guaranty variable interest entities’ liabilities	0	0
Payment of long-term debt	0	0
Net cash flows provided by (used in) financing activities	(103)	(128)
Effect of foreign exchange rate changes	0	0
Increase (decrease) in cash	(3)	0
Cash at beginning of period	8	4	4
Cash at end of period	5	4	8
Reportable Legal Entities [Member] | Other Entities [Member]
Condensed Cash Flow Statements, Captions [Line Items]
Net cash flows provided by (used in) operating activities	139	170
Fixed-maturity securities:
Purchases	(474)	(1,099)
Sales	725	1,195
Maturities	624	405
Net sales (purchases) of short-term investments	(136)	363
Net proceeds from financial guaranty variable entities’ assets	556	70
Investment in subsidiary	4	0
Acquisition of Radian Asset, net of cash acquired		(800)
Cash restricted for CIFG acquisition	(451)
Other	(12)	27
Net cash flows provided by (used in) investing activities	836	161
Cash flows from financing activities
Return of capital	(4)	(25)
Dividends paid	(314)	(226)
Repurchases of common stock	0	0
Share activity under option and incentive plans	(1)	0
Net paydowns of financial guaranty variable interest entities’ liabilities	(531)	(78)
Payment of long-term debt	(1)	(2)
Net cash flows provided by (used in) financing activities	(851)	(331)
Effect of foreign exchange rate changes	(3)	0
Increase (decrease) in cash	121	0
Cash at beginning of period	63	71	71
Cash at end of period	184	71	63
Consolidating Adjustments [Member]
Condensed Cash Flow Statements, Captions [Line Items]
Net cash flows provided by (used in) operating activities	(520)	(629)
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	(4)	(25)
Acquisition of Radian Asset, net of cash acquired		0
Cash restricted for CIFG acquisition	0
Other	0	0
Net cash flows provided by (used in) investing activities	(4)	(25)
Cash flows from financing activities
Return of capital	4	25
Dividends paid	520	629
Repurchases of common stock	0	0
Share activity under option and incentive plans	0	0
Net paydowns of financial guaranty variable interest entities’ liabilities	0	0
Payment of long-term debt	0	0
Net cash flows provided by (used in) financing activities	524	654
Effect of foreign exchange rate changes	0	0
Increase (decrease) in cash	0	0
Cash at beginning of period	0	0	0
Cash at end of period	$ 0	$ 0	$ 0