Summary of Revenues for Segments and Corporate and Other Activities (Detail) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Segment Reporting Information [Line Items]
Revenues	$ 2,150	$ 2,100	$ 6,171	$ 6,392
Segment, Continuing Operations | U.S. Mortgage Insurance
Segment Reporting Information [Line Items]
Revenues	186	161	537	497
Segment, Continuing Operations | Canada Mortgage Insurance
Segment Reporting Information [Line Items]
Revenues	156	124	463	429
Segment, Continuing Operations | Australia Mortgage Insurance
Segment Reporting Information [Line Items]
Revenues	115	122	333	360
Segment, Continuing Operations | Long-term Care Insurance
Segment Reporting Information [Line Items]
Revenues	980	949	3,051	2,769
Segment, Continuing Operations | Life Insurance
Segment Reporting Information [Line Items]
Revenues	418	455	953	1,419
Segment, Continuing Operations | Fixed Annuities
Segment Reporting Information [Line Items]
Revenues	218	221	613	683
Segment, Continuing Operations | U.S. Life Insurance
Segment Reporting Information [Line Items]
Revenues	1,616	1,625	4,617	4,871
Segment, Continuing Operations | Runoff
Segment Reporting Information [Line Items]
Revenues	84	53	218	209
Segment, Continuing Operations | Corporate and Other
Segment Reporting Information [Line Items]
Revenues	$ (7)	$ 15	$ 3	$ 26