Investments (Details) - USD ($) $ in Millions	Jun. 30, 2020	Dec. 31, 2019
Total Investments [Line Items]
Current investments	$ 2,596	$ 2,373
Long-term investments	18,594	17,314
Total investments	21,190	19,687
Debt securities available for sale
Total Investments [Line Items]
Current investments	2,396	2,251
Long-term investments	16,158	14,671
Total investments	18,554	16,922
Mortgage loans
Total Investments [Line Items]
Current investments	200	122
Long-term investments	938	1,091
Total investments	1,138	1,213
Other investments
Total Investments [Line Items]
Current investments	0	0
Long-term investments	1,498	1,552
Total investments	$ 1,498	$ 1,552