Investments - Schedule of Contractual Maturities of Investments (Details) - USD ($) $ in Millions	Sep. 30, 2021	Dec. 31, 2020
Amortized cost
Due in one year or less	$ 572
Due after one year through five years	3,722
Due after five years through ten years	3,445
Due after ten years	4,295
Total	12,034	$ 11,312
Fair value
Due in one year or less	580
Due after one year through five years	3,961
Due after five years through ten years	3,751
Due after ten years	4,616
Total	$ 12,908	$ 12,338
% of fair value
Due in one year or less	4.50%
Due after one year through five years	30.70%
Due after five years through ten years	29.10%
Due after ten years	35.70%
Total	100.00%