Insurance Company Regulatory Requirements - Dividends and Surplus Notes By Insurance Company Subsidiaries (Details) - USD ($) $ in Millions	3 Months Ended	9 Months Ended
Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Statutory Accounting Practices [Line Items]
Dividends paid			$ 53	$ 52
AGUS [Member] \| Affiliated Entity [Member] \| AGC [Member]
Statutory Accounting Practices [Line Items]
Dividends paid	$ 15	$ 15	66	38
AGM [Member] \| Affiliated Entity [Member] \| Municipal Assurance Corp [Member]
Statutory Accounting Practices [Line Items]
Repayment of surplus notes	0	0	0	100
AGMH [Member] \| Affiliated Entity [Member] \| AGM [Member]
Statutory Accounting Practices [Line Items]
Dividends paid	63	65	142	192
AGL [Member] \| Affiliated Entity [Member] \| Assured Guaranty Re [Member]
Statutory Accounting Practices [Line Items]
Dividends paid	45	35	125	85
Municipal Assurance Corp Holdings [Member] \| Affiliated Entity [Member] \| Municipal Assurance Corp [Member]
Statutory Accounting Practices [Line Items]
Dividends paid	12	0	36	0
Repayment of surplus notes	0	0	0	300
Redemption of common stock	$ 250	$ 0	$ 250	$ 0

Statutory Accounting Practices, Intercompany Transaction, Redemption of Common Stock

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- Definition

Statutory Accounting Practices, Intercompany Transaction, Repayment of Surplus Notes

+ References

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- Definition

Amount of cash outflow in the form of ordinary dividends to common shareholders of the parent entity.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 15
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=98514028&loc=d3e3291-108585

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