Investments - Schedule of Contractual Maturities of Investments (Details) - USD ($) $ in Millions	Mar. 31, 2020	Dec. 31, 2019
Amortized cost
Due in one year or less	$ 502
Due after one year through five years	3,132
Due after five years through ten years	3,833
Due after ten years	3,607
Total	11,074	$ 11,108
Fair value
Due in one year or less	502
Due after one year through five years	3,137
Due after five years through ten years	3,874
Due after ten years	3,827
Total	$ 11,340	$ 11,698
% of fair value
Due in one year or less	4.40%
Due after one year through five years	27.70%
Due after five years through ten years	34.20%
Due after ten years	33.70%
Total	100.00%