Summary of Goodwill Balance by Segment and Corporate and Other Activities (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended	3 Months Ended
Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2014	Sep. 30, 2012
Goodwill [Line Items]
Impairment losses	$ (849)us-gaap_GoodwillImpairmentLoss	$ 0us-gaap_GoodwillImpairmentLoss	$ (89)us-gaap_GoodwillImpairmentLoss
Foreign exchange translation	(2)	(1)
Gross goodwill	1,231us-gaap_GoodwillGross	1,233us-gaap_GoodwillGross	1,263us-gaap_GoodwillGross	1,231us-gaap_GoodwillGross
Accumulated impairment losses	(1,215)	(366)	(395)	(1,215)
Goodwill	16us-gaap_Goodwill	867us-gaap_Goodwill	868us-gaap_Goodwill	16us-gaap_Goodwill
U.S. Life Insurance
Goodwill [Line Items]
Impairment losses	(849)			(299)
Foreign exchange translation	0	0
Gross goodwill	1,034	1,034	1,034	1,034
Accumulated impairment losses	(1,034)	(185)	(185)	(1,034)
Goodwill	0	849	849	0
International Mortgage Insurance
Goodwill [Line Items]
Impairment losses	0
Foreign exchange translation	(2)	(1)
Gross goodwill	16	18	19	16
Accumulated impairment losses	0	0	0	0
Goodwill	16	18	19	16
U.S. Mortgage Insurance
Goodwill [Line Items]
Impairment losses	0
Foreign exchange translation	0	0
Gross goodwill	22	22	22	22
Accumulated impairment losses	(22)	(22)	(22)	(22)
Goodwill	0	0	0	0
International Protection
Goodwill [Line Items]
Impairment losses	0				(89)
Foreign exchange translation	0	0
Gross goodwill	89	89	89	89
Accumulated impairment losses	(89)	(89)	(89)	(89)
Goodwill	0	0	0	0
Runoff
Goodwill [Line Items]
Impairment losses	0
Foreign exchange translation	0	0
Gross goodwill	70	70	70	70
Accumulated impairment losses	(70)	(70)	(70)	(70)
Goodwill	0	0	0	0
Corporate and Other
Goodwill [Line Items]
Impairment losses	0
Foreign exchange translation	0	0
Gross goodwill	0	0	29	0
Accumulated impairment losses	0	0	(29)	0
Goodwill	$ 0	$ 0	$ 0	$ 0

Amount after accumulated impairment loss of an asset representing future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized.

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