Revenue Recognition - Contract with Customer, Asset and Liability (Details) - USD ($) $ in Millions	Sep. 30, 2021	Dec. 31, 2020
Capitalized Contract Cost [Line Items]
Customer receivables	$ 1,491	$ 1,889
Contract assets	71	108
Contract liabilities	703	950
Accounts receivable, gross	1,600	2,100
Allowance for doubtful accounts receivable	107	$ 174
Disposal Group, Held-for-sale, Not Discontinued Operations
Capitalized Contract Cost [Line Items]
Customer receivables	293
Contract assets	10
Contract liabilities	$ 165