Subsidiary Information - Condensed Consolidating Statement of Cash Flows (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2014	Mar. 31, 2013
Condensed financial statements
Net cash flows provided by (used in) operating activities	$ 101	$ (14)
Fixed-maturity securities:
Purchases	(517)	(510)
Sales	155	183
Maturities	148	283
Net sales (purchases) of short-term investments	184	88
Proceeds from paydowns on financial guaranty variable interest entities’ assets	286	138
Investment in subsidiary	0	0
Other	19	55
Net cash flows provided by (used in) investing activities	275	237
Cash flows from financing activities
Return of capital	0	0
Dividends paid	(20)	(19)
Repurchases of common stock	(35)	(39)
Share activity under option and incentive plans	0	(2)
Paydowns of financial guaranty variable interest entities’ liabilities	(281)	(167)
Repayment of long-term debt	(6)	(6)
Net cash flows provided by (used in) financing activities	(342)	(233)
Effect of exchange rate changes	1	(3)
Increase (decrease) in cash	35	(13)
Cash at beginning of period	184	138
Cash at end of period	219	125
Assured Guaranty Ltd. (Parent)
Condensed financial statements
Net cash flows provided by (used in) operating activities	58	36
Fixed-maturity securities:
Purchases	0	0
Sales	0	40
Maturities	0	18
Net sales (purchases) of short-term investments	(3)	(34)
Proceeds from paydowns on financial guaranty variable interest entities’ assets	0	0
Investment in subsidiary	0	0
Other	0	0
Net cash flows provided by (used in) investing activities	(3)	24
Cash flows from financing activities
Return of capital	0	0
Dividends paid	(20)	(19)
Repurchases of common stock	(35)	(39)
Share activity under option and incentive plans	0	(2)
Paydowns of financial guaranty variable interest entities’ liabilities	0	0
Repayment of long-term debt	0	0
Net cash flows provided by (used in) financing activities	(55)	(60)
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	0	1
Fixed-maturity securities:
Purchases	(1)	(1)
Sales	0	0
Maturities	0	0
Net sales (purchases) of short-term investments	0	0
Proceeds from paydowns on financial guaranty variable interest entities’ assets	0	0
Investment in subsidiary	0	0
Other	0	0
Net cash flows provided by (used in) investing activities	(1)	(1)
Cash flows from financing activities
Return of capital	0	0
Dividends paid	0	0
Repurchases of common stock	0	0
Share activity under option and incentive plans	0	0
Paydowns of financial guaranty variable interest entities’ liabilities	0	0
Repayment of long-term debt	0	0
Net cash flows provided by (used in) financing activities	0	0
Effect of exchange rate changes	0	0
Increase (decrease) in cash	(1)	0
Cash at beginning of period	67	13
Cash at end of period	66	13
AGMH
Condensed financial statements
Net cash flows provided by (used in) operating activities	(6)	(6)
Fixed-maturity securities:
Purchases	(3)	0
Sales	0	7
Maturities	0	1
Net sales (purchases) of short-term investments	(16)	(27)
Proceeds from paydowns on financial guaranty variable interest entities’ assets	0	0
Investment in subsidiary	25	25
Other	0	0
Net cash flows provided by (used in) investing activities	6	6
Cash flows from financing activities
Return of capital	0	0
Dividends paid	0	0
Repurchases of common stock	0	0
Share activity under option and incentive plans	0	0
Paydowns of financial guaranty variable interest entities’ liabilities	0	0
Repayment of long-term debt	0	0
Net cash flows provided by (used in) financing activities	0	0
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	111	(5)
Fixed-maturity securities:
Purchases	(513)	(509)
Sales	155	136
Maturities	148	264
Net sales (purchases) of short-term investments	203	149
Proceeds from paydowns on financial guaranty variable interest entities’ assets	286	138
Investment in subsidiary	0	0
Other	19	55
Net cash flows provided by (used in) investing activities	298	233
Cash flows from financing activities
Return of capital	(25)	(25)
Dividends paid	(62)	(40)
Repurchases of common stock	0	0
Share activity under option and incentive plans	0	0
Paydowns of financial guaranty variable interest entities’ liabilities	(281)	(167)
Repayment of long-term debt	(6)	(6)
Net cash flows provided by (used in) financing activities	(374)	(238)
Effect of exchange rate changes	1	(3)
Increase (decrease) in cash	36	(13)
Cash at beginning of period	117	125
Cash at end of period	153	112
Consolidating Adjustments
Condensed financial statements
Net cash flows provided by (used in) operating activities	(62)	(40)
Fixed-maturity securities:
Purchases	0	0
Sales	0	0
Maturities	0	0
Net sales (purchases) of short-term investments	0	0
Proceeds from paydowns on financial guaranty variable interest entities’ assets	0	0
Investment in subsidiary	(25)	(25)
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	62	40
Repurchases of common stock	0	0
Share activity under option and incentive plans	0	0
Paydowns of financial guaranty variable interest entities’ liabilities	0	0
Repayment of long-term debt	0	0
Net cash flows provided by (used in) financing activities	87	65
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