Account Balances of Variable Annuity Contract with Death or Living Benefit Guarantees Invested in Separate Account Investment Options (Detail) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Schedule of Fair Value of Separate Accounts by Major Category of Investment [Line Items]
Separate account investment	$ 3,879	$ 3,994
Balanced funds
Schedule of Fair Value of Separate Accounts by Major Category of Investment [Line Items]
Separate account investment	2,343	2,446
Equity funds
Schedule of Fair Value of Separate Accounts by Major Category of Investment [Line Items]
Separate account investment	1,016	1,079
Bond funds
Schedule of Fair Value of Separate Accounts by Major Category of Investment [Line Items]
Separate account investment	304	385
Money market funds
Schedule of Fair Value of Separate Accounts by Major Category of Investment [Line Items]
Separate account investment	$ 216	$ 84