Summary of Total Assets for Segments and Corporate and Other Activities (Detail) - USD ($) $ in Millions	Sep. 30, 2016	Dec. 31, 2015
Segment Reporting Information [Line Items]
Assets held for sale	$ 0	$ 127
Total assets	108,852	106,431
Segment, Continuing Operations
Segment Reporting Information [Line Items]
Total assets	108,852	106,304
Segment, Continuing Operations | U.S. Mortgage Insurance
Segment Reporting Information [Line Items]
Total assets	2,667	2,899
Segment, Continuing Operations | Canada Mortgage Insurance
Segment Reporting Information [Line Items]
Total assets	4,983	4,520
Segment, Continuing Operations | Australia Mortgage Insurance
Segment Reporting Information [Line Items]
Total assets	2,794	2,987
Segment, Continuing Operations | U.S. Life Insurance
Segment Reporting Information [Line Items]
Total assets	85,016	79,530
Segment, Continuing Operations | Runoff
Segment Reporting Information [Line Items]
Total assets	11,503	12,115
Segment, Continuing Operations | Corporate and Other
Segment Reporting Information [Line Items]
Total assets	$ 1,889	$ 4,253