Financial Instruments (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Fair Value, Liabilities Rollforward [Roll Forward]
Fair value of contingent consideration at December 31, 2018	$ 10
Additions: contingent consideration related to acquisitions completed during the period	0
Reductions: payments of contingent consideration	(4)
Changes in fair value (reflected in general and administrative expenses)	(2)
Fair value of contingent consideration at December 31, 2019	4
Deferred compensation plan assets (included in other non-current assets) | Fair Value Measurements Recurring Member
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Deferred compensation plan assets (included in other non-current assets)	2	$ 2
Deferred compensation plan assets (included in other non-current assets) | Fair Value Measurements Recurring Member | Level I
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Deferred compensation plan assets (included in other non-current assets)	2	2
Deferred compensation plan assets (included in other non-current assets) | Fair Value Measurements Recurring Member | Level II
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Deferred compensation plan assets (included in other non-current assets)	0	0
Deferred compensation plan assets (included in other non-current assets) | Fair Value Measurements Recurring Member | Level III
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Deferred compensation plan assets (included in other non-current assets)	0	0
Interest rate swap contracts | Fair Value Measurements Recurring Member
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Interest rate swaps (included in other non-current assets)		6
Interest rate swaps (included in other current and non-current liabilities)	47	16
Interest rate swap contracts | Fair Value Measurements Recurring Member | Level I
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Interest rate swaps (included in other non-current assets)		0
Interest rate swaps (included in other current and non-current liabilities)	0	0
Interest rate swap contracts | Fair Value Measurements Recurring Member | Level II
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Interest rate swaps (included in other non-current assets)		6
Interest rate swaps (included in other current and non-current liabilities)	47	16
Interest rate swap contracts | Fair Value Measurements Recurring Member | Level III
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Interest rate swaps (included in other non-current assets)		0
Interest rate swaps (included in other current and non-current liabilities)	0	0
Contingent consideration for acquisitions (included in accrued expenses and other current liabilities and other non-current liabilities) | Fair Value Measurements Recurring Member
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Contingent consideration for acquisitions (included in accrued expenses and other current liabilities and other non-current liabilities)	4	10
Contingent consideration for acquisitions (included in accrued expenses and other current liabilities and other non-current liabilities) | Fair Value Measurements Recurring Member | Level I
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Contingent consideration for acquisitions (included in accrued expenses and other current liabilities and other non-current liabilities)	0	0
Contingent consideration for acquisitions (included in accrued expenses and other current liabilities and other non-current liabilities) | Fair Value Measurements Recurring Member | Level II
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Contingent consideration for acquisitions (included in accrued expenses and other current liabilities and other non-current liabilities)	0	0
Contingent consideration for acquisitions (included in accrued expenses and other current liabilities and other non-current liabilities) | Fair Value Measurements Recurring Member | Level III
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Contingent consideration for acquisitions (included in accrued expenses and other current liabilities and other non-current liabilities)	$ 4	$ 10