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Basis of presentation and significant accounting policies and practices - Additional Information (Details) - USD ($) shares in Millions, $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018	Dec. 31, 2018
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Antidilutive securities excluded from computation of earnings per share, Amount (in shares)	6	4	7	4
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt, carrying value	$ 5,801		$ 5,801		$ 5,068
Level 2
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Long-term debt, estimated fair value	$ 6,320		$ 6,320