Summary of Revenues for Segments and Corporate and Other Activities (Detail) - USD ($) $ in Millions	3 Months Ended																12 Months Ended
	Dec. 31, 2016	[1]	Sep. 30, 2016	[1]	Jun. 30, 2016	[1]	Mar. 31, 2016	[1]	Dec. 31, 2015	[2]	Sep. 30, 2015	[2]	Jun. 30, 2015	[2]	Mar. 31, 2015	[2]	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Segment Reporting Information [Line Items]
Revenues	$ 2,198		$ 2,150		$ 2,236		$ 1,785		$ 2,156		$ 2,100		$ 2,157		$ 2,135		$ 8,369	$ 8,548	$ 8,729
Segment, Continuing Operations | U.S. Mortgage Insurance
Segment Reporting Information [Line Items]
Revenues																	726	665	639
Segment, Continuing Operations | Canada Mortgage Insurance
Segment Reporting Information [Line Items]
Revenues																	645	564	669
Segment, Continuing Operations | Australia Mortgage Insurance
Segment Reporting Information [Line Items]
Revenues																	440	474	537
Segment, Continuing Operations | Long-term Care Insurance
Segment Reporting Information [Line Items]
Revenues																	4,037	3,752	3,523
Segment, Continuing Operations | Life Insurance
Segment Reporting Information [Line Items]
Revenues																	1,381	1,902	1,981
Segment, Continuing Operations | Fixed Annuities
Segment Reporting Information [Line Items]
Revenues																	832	891	1,083
Segment, Continuing Operations | U.S. Life Insurance
Segment Reporting Information [Line Items]
Revenues																	6,250	6,545	6,587
Segment, Continuing Operations | Runoff
Segment Reporting Information [Line Items]
Revenues																	302	259	275
Segment, Continuing Operations | Corporate and Other
Segment Reporting Information [Line Items]
Revenues																	$ 6	$ 41	$ 22

[1] We completed our annual review of assumptions in the fourth quarter of 2016, which resulted in higher revenues of $6 million in our universal life insurance products. The updated assumptions reflected changes primarily to mortality experience in older age populations.

[2] We completed our annual review of assumptions in the fourth quarter of 2015, which primarily resulted in $12 million of higher revenue, in our universal and term universal life insurance products. The updated assumptions reflected changes to persistency, long-term interest rates, mortality and other refinements.