Aging of Past Due Commercial Mortgage Loans by Property Type (Detail) - USD ($) $ in Millions	Dec. 31, 2015	Dec. 31, 2014
Aging of Past Due Commercial Mortgage Loans [Line Items]
Commercial mortgage loans, recorded investment	$ 6,187	$ 6,123
% of total	100.00%	100.00%
Retail
Aging of Past Due Commercial Mortgage Loans [Line Items]
Commercial mortgage loans, recorded investment	$ 2,355	$ 2,150
% of total	38.00%	35.00%
Office
Aging of Past Due Commercial Mortgage Loans [Line Items]
Commercial mortgage loans, recorded investment	$ 1,516	$ 1,643
% of total	24.00%	27.00%
Industrial
Aging of Past Due Commercial Mortgage Loans [Line Items]
Commercial mortgage loans, recorded investment	$ 1,562	$ 1,597
% of total	25.00%	26.00%
Apartments
Aging of Past Due Commercial Mortgage Loans [Line Items]
Commercial mortgage loans, recorded investment	$ 465	$ 494
% of total	8.00%	8.00%
Mixed use/other
Aging of Past Due Commercial Mortgage Loans [Line Items]
Commercial mortgage loans, recorded investment	$ 289	$ 239
% of total	5.00%	4.00%
31-60 days past due
Aging of Past Due Commercial Mortgage Loans [Line Items]
Commercial mortgage loans, recorded investment	$ 6	$ 0
% of total	0.00%	0.00%
31-60 days past due | Retail
Aging of Past Due Commercial Mortgage Loans [Line Items]
Commercial mortgage loans, recorded investment	$ 0	$ 0
31-60 days past due | Office
Aging of Past Due Commercial Mortgage Loans [Line Items]
Commercial mortgage loans, recorded investment	6	0
31-60 days past due | Industrial
Aging of Past Due Commercial Mortgage Loans [Line Items]
Commercial mortgage loans, recorded investment	0	0
31-60 days past due | Apartments
Aging of Past Due Commercial Mortgage Loans [Line Items]
Commercial mortgage loans, recorded investment	0	0
31-60 days past due | Mixed use/other
Aging of Past Due Commercial Mortgage Loans [Line Items]
Commercial mortgage loans, recorded investment	0	0
61-90 days past due
Aging of Past Due Commercial Mortgage Loans [Line Items]
Commercial mortgage loans, recorded investment	$ 0	$ 0
% of total	0.00%	0.00%
61-90 days past due | Retail
Aging of Past Due Commercial Mortgage Loans [Line Items]
Commercial mortgage loans, recorded investment	$ 0	$ 0
61-90 days past due | Office
Aging of Past Due Commercial Mortgage Loans [Line Items]
Commercial mortgage loans, recorded investment	0	0
61-90 days past due | Industrial
Aging of Past Due Commercial Mortgage Loans [Line Items]
Commercial mortgage loans, recorded investment	0	0
61-90 days past due | Apartments
Aging of Past Due Commercial Mortgage Loans [Line Items]
Commercial mortgage loans, recorded investment	0	0
61-90 days past due | Mixed use/other
Aging of Past Due Commercial Mortgage Loans [Line Items]
Commercial mortgage loans, recorded investment	0	0
Greater than 90 days past due
Aging of Past Due Commercial Mortgage Loans [Line Items]
Commercial mortgage loans, recorded investment	$ 5	$ 8
% of total	0.00%	0.00%
Greater than 90 days past due | Retail
Aging of Past Due Commercial Mortgage Loans [Line Items]
Commercial mortgage loans, recorded investment	$ 0	$ 0
Greater than 90 days past due | Office
Aging of Past Due Commercial Mortgage Loans [Line Items]
Commercial mortgage loans, recorded investment	5	6
Greater than 90 days past due | Industrial
Aging of Past Due Commercial Mortgage Loans [Line Items]
Commercial mortgage loans, recorded investment	0	2
Greater than 90 days past due | Apartments
Aging of Past Due Commercial Mortgage Loans [Line Items]
Commercial mortgage loans, recorded investment	0	0
Greater than 90 days past due | Mixed use/other
Aging of Past Due Commercial Mortgage Loans [Line Items]
Commercial mortgage loans, recorded investment	0	0
Total past due
Aging of Past Due Commercial Mortgage Loans [Line Items]
Commercial mortgage loans, recorded investment	$ 11	$ 8
% of total	0.00%	0.00%
Total past due | Retail
Aging of Past Due Commercial Mortgage Loans [Line Items]
Commercial mortgage loans, recorded investment	$ 0	$ 0
Total past due | Office
Aging of Past Due Commercial Mortgage Loans [Line Items]
Commercial mortgage loans, recorded investment	11	6
Total past due | Industrial
Aging of Past Due Commercial Mortgage Loans [Line Items]
Commercial mortgage loans, recorded investment	0	2
Total past due | Apartments
Aging of Past Due Commercial Mortgage Loans [Line Items]
Commercial mortgage loans, recorded investment	0	0
Total past due | Mixed use/other
Aging of Past Due Commercial Mortgage Loans [Line Items]
Commercial mortgage loans, recorded investment	0	0
Current
Aging of Past Due Commercial Mortgage Loans [Line Items]
Commercial mortgage loans, recorded investment	$ 6,176	$ 6,115
% of total	100.00%	100.00%
Current | Retail
Aging of Past Due Commercial Mortgage Loans [Line Items]
Commercial mortgage loans, recorded investment	$ 2,355	$ 2,150
Current | Office
Aging of Past Due Commercial Mortgage Loans [Line Items]
Commercial mortgage loans, recorded investment	1,505	1,637
Current | Industrial
Aging of Past Due Commercial Mortgage Loans [Line Items]
Commercial mortgage loans, recorded investment	1,562	1,595
Current | Apartments
Aging of Past Due Commercial Mortgage Loans [Line Items]
Commercial mortgage loans, recorded investment	465	494
Current | Mixed use/other
Aging of Past Due Commercial Mortgage Loans [Line Items]
Commercial mortgage loans, recorded investment	$ 289	$ 239