Revenues and Contract Costs - Schedule of Cost Incurred to Obtain or Fulfill Contracts with Customers (Details) - USD ($) $ in Millions	Sep. 30, 2021	Dec. 31, 2020
Capitalized Contract Cost [Line Items]
Cost incurred to obtain or fulfill contracts with customers	$ 4,517	$ 4,542
Minimum
Capitalized Contract Cost [Line Items]
Deferred contract cost, amortization period	2 years
Maximum
Capitalized Contract Cost [Line Items]
Deferred contract cost, amortization period	6 years
Prepaid expenses and other
Capitalized Contract Cost [Line Items]
Cost incurred to obtain or fulfill contracts with customers	$ 2,366	2,472
Other assets
Capitalized Contract Cost [Line Items]
Cost incurred to obtain or fulfill contracts with customers	$ 2,151	$ 2,070