Investments - Total Investment Schedule (Details) - USD ($) $ in Millions	Mar. 31, 2021	Dec. 31, 2020
Total Investments [Line Items]
Current investments	$ 3,190	$ 3,000
Long-term investments	21,025	20,812
Total investments	24,215	23,812
Debt securities available for sale
Total Investments [Line Items]
Current investments	3,003	2,774
Long-term investments	18,501	18,414
Total investments	21,504	21,188
Mortgage loans
Total Investments [Line Items]
Current investments	187	226
Long-term investments	810	821
Total investments	997	1,047
Other investments
Total Investments [Line Items]
Current investments	0	0
Long-term investments	1,714	1,577
Total investments	$ 1,714	$ 1,577