Guaranteed Benefit Features - Separate Accounts by Investment Type (Details) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Equity funds
Fair Value, Separate Account Investment [Line Items]
Equity securities (including mutual funds)	$ 2,000	$ 1,904
Bond funds
Fair Value, Separate Account Investment [Line Items]
Equity securities (including mutual funds)	190	184
Balanced funds
Fair Value, Separate Account Investment [Line Items]
Equity securities (including mutual funds)	341	329
Money market funds
Fair Value, Separate Account Investment [Line Items]
Equity securities (including mutual funds)	49	46
Other
Fair Value, Separate Account Investment [Line Items]
Equity securities (including mutual funds)	10	10
Equity securities
Fair Value, Separate Account Investment [Line Items]
Equity securities (including mutual funds)	2,590	2,473
Fixed income securities
Fair Value, Separate Account Investment [Line Items]
Equity securities (including mutual funds)	$ 8,400	$ 7,400