Subsidiary Information (Details 3) (USD $) In Millions, unless otherwise specified	6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Mar. 31, 2012
Condensed financial statements
Net cash flows provided by (used in) operating activities	$ 122	$ 162
Fixed maturity securities:
Purchases	(987)	(924)
Sales	632	526
Maturities	446	515
Net sales (purchases) of short-term investments	(126)	(108)
Net proceeds from paydowns on financial guaranty variable interest entities’ assets	440	283
Acquisition of MAC, net of cash acquired	0	(91)
Intercompany debt		0
Investment in subsidiary	0	0
Other	67	72
Net cash flows provided by (used in) investing activities	472	273
Net cash flows used in investing activities
Proceeds from issuance of common stock	0	173
Return of capital	0	0
Dividends paid	(38)	(33)
Repurchases of common stock	(244)	(24)
Share activity under option and incentive plans	(1)	(2)
Net paydowns of financial guaranty variable interest entities’ liabilities	(289)	(389)
Repayment of long-term debt	(13)	(196)
Intercompany debt		0
Net cash flows provided by (used in) financing activities	(585)	(471)
Effect of exchange rate changes	(4)	(4)
Increase (decrease) in cash	5	(40)
Cash at beginning of period	138	215	175
Cash at end of period	143	175	175
Assured Guaranty Ltd. (Parent)
Condensed financial statements
Net cash flows provided by (used in) operating activities	86	56
Fixed maturity securities:
Purchases	0	(92)
Sales	171	0
Maturities	21	0
Net sales (purchases) of short-term investments	5	(78)
Net proceeds from paydowns on financial guaranty variable interest entities’ assets	0	0
Acquisition of MAC, net of cash acquired		0
Intercompany debt		0
Investment in subsidiary	0	0
Other	0	0
Net cash flows provided by (used in) investing activities	197	(170)
Net cash flows used in investing activities
Proceeds from issuance of common stock		173
Return of capital	0	0
Dividends paid	(38)	(33)
Repurchases of common stock	(244)	(24)
Share activity under option and incentive plans	(1)	(2)
Net paydowns of financial guaranty variable interest entities’ liabilities	0	0
Repayment of long-term debt	0	0
Intercompany debt		0
Net cash flows provided by (used in) financing activities	(283)	114
Effect of exchange rate changes	0	0
Increase (decrease) in cash	0	0
Cash at beginning of period	0	0
Cash at end of period	0	0
AGUS (Issuer)
Condensed financial statements
Net cash flows provided by (used in) operating activities	43	24
Fixed maturity securities:
Purchases	0	(1)
Sales	1	0
Maturities	0	0
Net sales (purchases) of short-term investments	(56)	27
Net proceeds from paydowns on financial guaranty variable interest entities’ assets	0	0
Acquisition of MAC, net of cash acquired		(91)
Intercompany debt		0
Investment in subsidiary	0	0
Other	0	0
Net cash flows provided by (used in) investing activities	(55)	(65)
Net cash flows used in investing activities
Proceeds from issuance of common stock		0
Return of capital	0	0
Dividends paid	0	0
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
Repayment of long-term debt	0	(173)
Intercompany debt		173
Net cash flows provided by (used in) financing activities	0	0
Effect of exchange rate changes	0	0
Increase (decrease) in cash	(12)	(41)
Cash at beginning of period	13	72
Cash at end of period	1	31
AGMH
Condensed financial statements
Net cash flows provided by (used in) operating activities	14	21
Fixed maturity securities:
Purchases	(23)	(11)
Sales	19	1
Maturities	2	2
Net sales (purchases) of short-term investments	1	17
Net proceeds from paydowns on financial guaranty variable interest entities’ assets	0	0
Acquisition of MAC, net of cash acquired		0
Intercompany debt		0
Investment in subsidiary	25	50
Other	0	0
Net cash flows provided by (used in) investing activities	24	59
Net cash flows used in investing activities
Proceeds from issuance of common stock		0
Return of capital	0	0
Dividends paid	(38)	(80)
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
Repayment of long-term debt	0	0
Intercompany debt		0
Net cash flows provided by (used in) financing activities	(38)	(80)
Effect of exchange rate changes	0	0
Increase (decrease) in cash	0	0
Cash at beginning of period	0	0
Cash at end of period	0	0
Other Subsidiaries
Condensed financial statements
Net cash flows provided by (used in) operating activities	172	296
Fixed maturity securities:
Purchases	(1,029)	(820)
Sales	506	525
Maturities	423	513
Net sales (purchases) of short-term investments	(76)	(74)
Net proceeds from paydowns on financial guaranty variable interest entities’ assets	440	283
Acquisition of MAC, net of cash acquired		0
Intercompany debt		(173)
Investment in subsidiary	0	0
Other	67	72
Net cash flows provided by (used in) investing activities	331	326
Net cash flows used in investing activities
Proceeds from issuance of common stock		0
Return of capital	(25)	(50)
Dividends paid	(155)	(155)
Repurchases of common stock	0	0
Share activity under option and incentive plans	0	0
Net paydowns of financial guaranty variable interest entities’ liabilities	(289)	(389)
Repayment of long-term debt	(13)	(23)
Intercompany debt		0
Net cash flows provided by (used in) financing activities	(482)	(617)
Effect of exchange rate changes	(4)	(4)
Increase (decrease) in cash	17	1
Cash at beginning of period	125	143
Cash at end of period	142	144
Consolidating Adjustments
Condensed financial statements
Net cash flows provided by (used in) operating activities	(193)	(235)
Fixed maturity securities:
Purchases	65	0
Sales	(65)	0
Maturities	0	0
Net sales (purchases) of short-term investments	0	0
Net proceeds from paydowns on financial guaranty variable interest entities’ assets	0	0
Acquisition of MAC, net of cash acquired		0
Intercompany debt		173
Investment in subsidiary	(25)	(50)
Other	0	0
Net cash flows provided by (used in) investing activities	(25)	123
Net cash flows used in investing activities
Proceeds from issuance of common stock		0
Return of capital	25	50
Dividends paid	193	235
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
Repayment of long-term debt	0	0
Intercompany debt		(173)
Net cash flows provided by (used in) financing activities	218	112
Effect of exchange rate changes	0	0
Increase (decrease) in cash	0	0
Cash at beginning of period	0	0
Cash at end of period	$ 0	$ 0