Long-Term Debt - Narrative (Details) - USD ($) $ in Millions	1 Months Ended	3 Months Ended
	Jul. 31, 2021	Jun. 30, 2021	Mar. 31, 2021	Dec. 31, 2020
Long-term Debt
Repayments of near-term maturities of debt		$ 0	$ 174
Unamortized premium associated with tender and purchase		707		$ 748
Long-term debt, gross		35,061		35,235
Subsequent Event
Long-term Debt
Long-term debt, gross	$ 32,000
July Tender and Purchase | Senior Notes | Subsequent Event
Long-term Debt
Tender and purchase	3,100
Unamortized premium associated with tender and purchase	$ 90
Estimate of Fair Value | Level 1
Long-term Debt
Fair value of long-term debt		$ 36,800		$ 33,800