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Insurance In Force (Summary Of Components Of Financial Guarantee Net Premiums Earned, Including Premiums Assumed From And Ceded To Other Companies) (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Insurance in Force [Abstract]
Direct	$ 205	$ 305	$ 379
Assumed	2	2	2
Gross	207	307	381
Ceded premiums earned	(6)	(7)	(9)
Premiums earned (net of ceded premiums of $6, $7 and $9)	$ 201	$ 300	$ 372

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Gross Premium Earned Financial Guarantee

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Amount of earned premiums assumed from other entities.

+ References

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 235
-Section S99
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