Investments - Schedule of Contractual Maturities of Investments (Details) - USD ($) $ in Millions	Jun. 30, 2021	Dec. 31, 2020
Amortized cost
Due in one year or less	$ 516
Due after one year through five years	3,669
Due after five years through ten years	3,574
Due after ten years	4,068
Total	11,827	$ 11,312
Fair value
Due in one year or less	524
Due after one year through five years	3,924
Due after five years through ten years	3,904
Due after ten years	4,437
Total	$ 12,789	$ 12,338
% of fair value
Due in one year or less	4.10%
Due after one year through five years	30.70%
Due after five years through ten years	30.50%
Due after ten years	34.70%
Total	100.00%