Revenue Recognition - Contract with Customer, Asset and Liability (Details) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018	Jan. 01, 2018
Revenue from Contract with Customer [Abstract]
Customer receivables	$ 2,194		$ 2,346
Contract liabilities	1,028		860
Contract assets	130		$ 140
Accounts receivable, gross	2,300	$ 2,500
Allowance for doubtful accounts	$ 94	$ 132