Investments - Schedule of Contractual Maturities of Investments (Details) - USD ($) $ in Millions	Mar. 31, 2021	Dec. 31, 2020
Amortized cost
Due in one year or less	$ 585
Due after one year through five years	3,563
Due after five years through ten years	3,688
Due after ten years	3,642
Total	11,478	$ 11,312
Fair value
Due in one year or less	593
Due after one year through five years	3,799
Due after five years through ten years	3,987
Due after ten years	3,929
Total	$ 12,308	$ 12,338
% of fair value
Due in one year or less	4.80%
Due after one year through five years	30.90%
Due after five years through ten years	32.40%
Due after ten years	31.90%
Total	100.00%