Net Investment Income (Detail) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Net Investment Income [Line Items]
Gross investment income before expenses and fees	$ 853	$ 826
Expenses and fees	(24)	(22)
Net investment income	829	804
Fixed maturity securities—taxable
Net Investment Income [Line Items]
Gross investment income before expenses and fees	643	635
Fixed maturity securities—non-taxable
Net Investment Income [Line Items]
Gross investment income before expenses and fees	2	3
Equity Securities
Net Investment Income [Line Items]
Gross investment income before expenses and fees	9	10
Commercial mortgage loans
Net Investment Income [Line Items]
Gross investment income before expenses and fees	81	82
Restricted commercial mortgage loans related to securitization entities
Net Investment Income [Line Items]
Gross investment income before expenses and fees	1	2
Policy Loans
Net Investment Income [Line Items]
Gross investment income before expenses and fees	46	43
Other invested assets
Net Investment Income [Line Items]
Gross investment income before expenses and fees	59	39
Cash, cash equivalents, restricted cash and short-term investments
Net Investment Income [Line Items]
Gross investment income before expenses and fees	$ 12	$ 12