Subsidiary Information - Condensed Consolidating Statement of Cash Flows (Details) - USD ($) $ in Millions	6 Months Ended		12 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Dec. 31, 2014
Condensed Cash Flow Statements, Captions [Line Items]
Net cash flows provided by (used in) operating activities	$ 105	$ 222
Fixed-maturity securities:
Purchases	(1,172)	(1,357)
Sales	1,381	444
Maturities	411	397
Net sales (purchases) of short-term investments	382	(51)
Net proceeds from financial guaranty variable entities’ assets	70	315
Intercompany debt	0	0
Investment in subsidiary	0	0
Acquisition of Radian Asset, net of cash acquired	(800)	0
Other	27	23
Net cash flows provided by (used in) investing activities	299	(229)
Cash flows from financing activities
Return of capital	0	0
Dividends paid	(37)	(40)
Repurchases of common stock	(285)	(212)
Share activity under option and incentive plans	(2)	1
Net paydowns of financial guaranty variable interest entities’ liabilities	(78)	(311)
Proceeds from issuance of long-term debt	0	496
Payment of long-term debt	(2)	(7)
Intercompany debt	0	0
Net cash flows provided by (used in) financing activities	(404)	(73)
Effect of foreign exchange rate changes	0	2
Increase (decrease) in cash	0	(78)
Cash at beginning of period	75	184	$ 184
Cash at end of period	75	106	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	343	264
Fixed-maturity securities:
Purchases	0	0
Sales	0	0
Maturities	0	0
Net sales (purchases) of short-term investments	(19)	(13)
Net proceeds from financial guaranty variable entities’ assets	0	0
Intercompany debt	0	0
Investment in subsidiary	0	0
Acquisition of Radian Asset, net of cash acquired	0
Other	0	0
Net cash flows provided by (used in) investing activities	(19)	(13)
Cash flows from financing activities
Return of capital	0	0
Dividends paid	(37)	(40)
Repurchases of common stock	(285)	(212)
Share activity under option and incentive plans	(2)	1
Net paydowns of financial guaranty variable interest entities’ liabilities	0	0
Proceeds from issuance of long-term debt		0
Payment of long-term debt	0	0
Intercompany debt	0	0
Net cash flows provided by (used in) financing activities	(324)	(251)
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
Reportable Legal Entities [Member] | AGUS (Issuer) [Member]
Condensed Cash Flow Statements, Captions [Line Items]
Net cash flows provided by (used in) operating activities	138	68
Fixed-maturity securities:
Purchases	(67)	(356)
Sales	159	126
Maturities	6	3
Net sales (purchases) of short-term investments	39	(199)
Net proceeds from financial guaranty variable entities’ assets	0	0
Intercompany debt	0	0
Investment in subsidiary	0	0
Acquisition of Radian Asset, net of cash acquired	0
Other	0	0
Net cash flows provided by (used in) investing activities	137	(426)
Cash flows from financing activities
Return of capital	0	0
Dividends paid	(275)	(200)
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
Proceeds from issuance of long-term debt		496
Payment of long-term debt	0	0
Intercompany debt	0	0
Net cash flows provided by (used in) financing activities	(275)	296
Effect of foreign exchange rate changes	0	0
Increase (decrease) in cash	0	(62)
Cash at beginning of period	0	67	67
Cash at end of period	0	5	0
Reportable Legal Entities [Member] | AGMH (Issuer) [Member]
Condensed Cash Flow Statements, Captions [Line Items]
Net cash flows provided by (used in) operating activities	83	32
Fixed-maturity securities:
Purchases	(6)	(6)
Sales	27	7
Maturities	0	1
Net sales (purchases) of short-term investments	(1)	6
Net proceeds from financial guaranty variable entities’ assets	0	0
Intercompany debt	0	0
Investment in subsidiary	25	25
Acquisition of Radian Asset, net of cash acquired	0
Other	0	0
Net cash flows provided by (used in) investing activities	45	33
Cash flows from financing activities
Return of capital	0	0
Dividends paid	(128)	(65)
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
Proceeds from issuance of long-term debt		0
Payment of long-term debt	0	0
Intercompany debt	0	0
Net cash flows provided by (used in) financing activities	(128)	(65)
Effect of foreign exchange rate changes	0	0
Increase (decrease) in cash	0	0
Cash at beginning of period	4	0	0
Cash at end of period	4	0	4
Reportable Legal Entities [Member] | Other Entities [Member]
Condensed Cash Flow Statements, Captions [Line Items]
Net cash flows provided by (used in) operating activities	170	275
Fixed-maturity securities:
Purchases	(1,099)	(995)
Sales	1,195	311
Maturities	405	393
Net sales (purchases) of short-term investments	363	155
Net proceeds from financial guaranty variable entities’ assets	70	315
Intercompany debt	0	0
Investment in subsidiary	0	0
Acquisition of Radian Asset, net of cash acquired	(800)
Other	27	23
Net cash flows provided by (used in) investing activities	161	202
Cash flows from financing activities
Return of capital	(25)	(25)
Dividends paid	(226)	(152)
Repurchases of common stock	0	0
Share activity under option and incentive plans	0	0
Net paydowns of financial guaranty variable interest entities’ liabilities	(78)	(311)
Proceeds from issuance of long-term debt		0
Payment of long-term debt	(2)	(7)
Intercompany debt	0	0
Net cash flows provided by (used in) financing activities	(331)	(495)
Effect of foreign exchange rate changes	0	2
Increase (decrease) in cash	0	(16)
Cash at beginning of period	71	117	117
Cash at end of period	71	101	71
Consolidating Adjustments [Member]
Condensed Cash Flow Statements, Captions [Line Items]
Net cash flows provided by (used in) operating activities	(629)	(417)
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
Intercompany debt	0	0
Investment in subsidiary	(25)	(25)
Acquisition of Radian Asset, net of cash acquired	0
Other	0	0
Net cash flows provided by (used in) investing activities	(25)	(25)
Cash flows from financing activities
Return of capital	25	25
Dividends paid	629	417
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
Proceeds from issuance of long-term debt		0
Payment of long-term debt	0	0
Intercompany debt	0	0
Net cash flows provided by (used in) financing activities	654	442
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