Investments - Total Investment Schedule (Details) - USD ($) $ in Millions	Sep. 30, 2021	Dec. 31, 2020
Total Investments [Line Items]
Current	$ 3,015	$ 3,000
Long-term	22,370	20,812
Total	25,385	23,812
Debt securities available for sale
Total Investments [Line Items]
Current	2,859	2,774
Long-term	19,715	18,414
Total	22,574	21,188
Mortgage loans
Total Investments [Line Items]
Current	110	226
Long-term	824	821
Total	934	1,047
Other investments
Total Investments [Line Items]
Current	46	0
Long-term	1,831	1,577
Total	$ 1,877	$ 1,577