Investments (Details) - USD ($) $ in Millions	Mar. 31, 2020	Dec. 31, 2019
Total Investments [Line Items]
Current investments	$ 2,632	$ 2,373
Long-term investments	16,840	17,314
Total investments	19,472	19,687
Debt securities available for sale
Total Investments [Line Items]
Current investments	2,451	2,251
Long-term investments	14,266	14,671
Total investments	16,717	16,922
Mortgage loans
Total Investments [Line Items]
Current investments	181	122
Long-term investments	983	1,091
Total investments	1,164	1,213
Other investments
Total Investments [Line Items]
Current investments	0	0
Long-term investments	1,591	1,552
Total investments	$ 1,591	$ 1,552