Contracts Accounted for as Insurance - Scheduled Net Earned Premiums Insurance Contracts (Details) $ in Millions	Mar. 31, 2018 USD ($)
Financial Guarantee Insurance Premiums [Line Items]
Other deferred premium revenue	$ 8
Financial Guarantee Insurance Product Line [Member]
Financial Guarantee Insurance Premiums [Line Items]
2018 (April 1 - June 30)	87
2018 (July 1 - September 30)	84
2018 (October 1 - December 31)	81
Subtotal 2018	252
2019	292
2020	268
2021	244
2022	222
2023-2027	864
2028-2032	569
2033-2037	330
After 2037	286
Deferred premium revenue, net	3,327
Future accretion	181
Total future net earned premiums	3,508
Variable Interest Entity, Primary Beneficiary [Member]
Financial Guarantee Insurance Premiums [Line Items]
Deferred premium revenue, net	$ 73

Financial Guarantee Contracts, Other Deferred Premium Revenue

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- Definition

For financial guarantee insurance contracts, the discounted amount of premium revenue expected to be recognized over the term of the contract period.

+ References

No definition available.

+ Details

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- Definition

For financial guarantee insurance contracts, the undiscounted amount of premium revenue expected to be recognized over the term of the contract period.

+ References

No definition available.

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- Definition

Financial Guarantee Insurance Contracts, Future Expected Premium Revenue to be Recognized, Fiscal Year

+ References

No definition available.

+ Details

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- Definition

For financial guarantee insurance contracts, the amount of premium revenue expected to be recognized beyond the twentieth year following the statement of financial position reporting date.

+ References

No definition available.

+ Details

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- Definition

Amount of unearned premium revenue in the statement of financial position for financial guaranty insurance contracts, net of the unexpired portion of premiums ceded and before adjustment for loss claims paid but not yet expensed.

+ References

No definition available.

+ Details

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- Definition

[Line Items] for Financial Guarantee Insurance Premiums [Table]

+ References

No definition available.

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- Definition

Amount of premium revenue under financial guarantee insurance contracts expected to be recognized in the fourth fiscal quarter following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 605
-Section 50
-Paragraph 4
-Subparagraph (b)(1)
-URI http://asc.fasb.org/extlink&oid=6933581&loc=SL5749298-161291

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- Definition

Amount of premium revenue under financial guarantee insurance contracts expected to be recognized in the second fiscal quarter following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

+ References

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- Definition

Amount of premium revenue under financial guarantee insurance contracts expected to be recognized in the third fiscal quarter following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

+ References

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- Definition

Amount of premium revenue under financial guarantee insurance contracts expected to be recognized in the eleventh through fifteenth fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 605
-Section 50
-Paragraph 4
-Subparagraph (b)(2)
-URI http://asc.fasb.org/extlink&oid=6933581&loc=SL5749298-161291

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- Definition

Amount of premium revenue under financial guarantee insurance contracts expected to be recognized in the sixteenth through twentieth fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 605
-Section 50
-Paragraph 4
-Subparagraph (b)(2)
-URI http://asc.fasb.org/extlink&oid=6933581&loc=SL5749298-161291

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- Definition

Amount of premium revenue under financial guarantee insurance contracts expected to be recognized in the sixth through tenth fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 605
-Section 50
-Paragraph 4
-Subparagraph (b)(2)
-URI http://asc.fasb.org/extlink&oid=6933581&loc=SL5749298-161291

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- Definition

Amount of premium revenue under financial guarantee insurance contracts expected to be recognized in the fifth fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

+ References

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- Definition

Amount of premium revenue under financial guarantee insurance contracts expected to be recognized in the second fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

+ References

+ Details

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- Definition

Amount of premium revenue under financial guarantee insurance contracts expected to be recognized in the fourth fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

+ References

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- Definition

Amount of premium revenue under financial guarantee insurance contracts expected to be recognized in the third fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

+ References

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