Accounting Policies - Narrative (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Jun. 30, 2020	Jan. 01, 2020	Dec. 31, 2019
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Change in Accounting Principle, Accounting Standards Update, Adopted [true false]			true
Change in Accounting Principle, Accounting Standards Update, Adoption Date			Jan. 01, 2020
Accounting Standards Update [Extensible List]	us-gaap:AccountingStandardsUpdate201613Member	us-gaap:AccountingStandardsUpdate201602Member	us-gaap:AccountingStandardsUpdate201613Member
Retained earnings			$ 4,748		$ 6,113
Accounts receivable			1,727		1,941
Deferred income taxes			$ 1,434		$ 1,527
Accounting Standards Update 2016-13 | Restatement Adjustment
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Retained earnings				$ (12)
Accounts receivable				(15)
Deferred income taxes				$ 3