Investments - Debt Securities by Maturity (Details) - USD ($) $ in Millions	Sep. 30, 2021	Dec. 31, 2020
Amortized Cost
Less than one year	$ 1,056
One year through five years	7,123
After five years through ten years	4,492
Greater than ten years	4,190
Amortized Cost	21,317	$ 19,396
Fair Value
Less than one year	1,071
One year through five years	7,390
After five years through ten years	4,718
Greater than ten years	4,855
Total	22,574	21,188
Residential mortgage-backed securities
Amortized Cost
Debt securities, maturity, without single maturity date	849
Amortized Cost	849	673
Fair Value
Debt securities, maturity, without single maturity date	863
Total	863	705
Commercial mortgage-backed securities
Amortized Cost
Debt securities, maturity, without single maturity date	1,160
Amortized Cost	1,160	962
Fair Value
Debt securities, maturity, without single maturity date	1,209
Total	1,209	1,046
Other asset-backed securities
Amortized Cost
Debt securities, maturity, without single maturity date	2,447
Amortized Cost	2,447	2,369
Fair Value
Debt securities, maturity, without single maturity date	2,468
Total	$ 2,468	$ 2,403