Condensed Consolidating Financial Information - Condensed Consolidating Statement of Cash Flows (Details) - USD ($) $ in Millions	3 Months Ended	6 Months Ended
Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Condensed Statements of Cash Flows, Captions [Line Items]
Net cash flow provided by (used for) operating activities		$ 83.5	$ 68.2
Capital expenditures		(39.6)	(46.4)
Acquisitions		(34.4)	(4.3)
MTA franchise rights		(10.7)	(6.1)
Net proceeds from dispositions		2.2	3.4
Net cash flow provided by (used for) investing activities		(82.5)	(53.4)
Proceeds from long-term debt borrowings		705.0	79.0
Repayments of long-term debt borrowings		(55.0)	(10.0)
Proceeds from borrowings under short-term debt facilities		30.0	75.0
Repayments of borrowings under short-term debt facilities		(190.0)	(55.0)
Payments of deferred financing costs		(8.6)	(0.1)
Proceeds from shares issued under the ATM Program		50.9	0.0
Taxes withheld for stock-based compensation		(7.7)	(8.1)
Dividends		(103.9)	(102.0)
Intercompany		0.0	0.0
Net cash flow provided by (used for) financing activities		420.7	(21.2)
Effect of exchange rate changes on cash, cash equivalents and restricted cash		0.4	(0.2)
Net increase (decrease) in cash, cash equivalents and restricted cash		422.1	(6.6)
Cash, cash equivalents and restricted cash, beginning of period	$ 41.7	54.1	48.3
Cash, cash equivalents and restricted cash, end of period	41.7	476.2	41.7
Eliminations
Condensed Statements of Cash Flows, Captions [Line Items]
Net cash flow provided by (used for) operating activities		0.0	0.0
Capital expenditures		0.0	0.0
Acquisitions		0.0	0.0
MTA franchise rights		0.0	0.0
Net proceeds from dispositions		0.0	0.0
Net cash flow provided by (used for) investing activities		0.0	0.0
Proceeds from long-term debt borrowings		0.0	0.0
Repayments of long-term debt borrowings		0.0	0.0
Proceeds from borrowings under short-term debt facilities		0.0	0.0
Repayments of borrowings under short-term debt facilities		0.0	0.0
Payments of deferred financing costs		0.0	0.0
Proceeds from shares issued under the ATM Program		0.0
Taxes withheld for stock-based compensation		0.0	0.0
Dividends		0.0	0.0
Intercompany		0.0	0.0
Net cash flow provided by (used for) financing activities		0.0	0.0
Effect of exchange rate changes on cash, cash equivalents and restricted cash		0.0	0.0
Net increase (decrease) in cash, cash equivalents and restricted cash		0.0	0.0
Cash, cash equivalents and restricted cash, beginning of period		0.0	0.0
Cash, cash equivalents and restricted cash, end of period	0.0	0.0	0.0
Parent Company
Condensed Statements of Cash Flows, Captions [Line Items]
Net cash flow provided by (used for) operating activities		(0.8)	(0.8)
Capital expenditures		0.0	0.0
Acquisitions		0.0	0.0
MTA franchise rights		0.0	0.0
Net proceeds from dispositions		0.0	0.0
Net cash flow provided by (used for) investing activities		0.0	0.0
Proceeds from long-term debt borrowings		0.0	0.0
Repayments of long-term debt borrowings		0.0	0.0
Proceeds from borrowings under short-term debt facilities		0.0	0.0
Repayments of borrowings under short-term debt facilities		0.0	0.0
Payments of deferred financing costs		0.0	0.0
Proceeds from shares issued under the ATM Program		50.9
Taxes withheld for stock-based compensation		0.0	0.0
Dividends		(102.8)	(100.6)
Intercompany		52.7	101.4
Net cash flow provided by (used for) financing activities		0.8	0.8
Effect of exchange rate changes on cash, cash equivalents and restricted cash		0.0	0.0
Net increase (decrease) in cash, cash equivalents and restricted cash		0.0	0.0
Cash, cash equivalents and restricted cash, beginning of period		0.0	0.0
Cash, cash equivalents and restricted cash, end of period	0.0	0.0	0.0
Subsidiary Issuer
Condensed Statements of Cash Flows, Captions [Line Items]
Net cash flow provided by (used for) operating activities		(58.6)	(55.6)
Capital expenditures		0.0	0.0
Acquisitions		0.0	0.0
MTA franchise rights		0.0	0.0
Net proceeds from dispositions		0.0	0.0
Net cash flow provided by (used for) investing activities		0.0	0.0
Proceeds from long-term debt borrowings		705.0	79.0
Repayments of long-term debt borrowings		(55.0)	(10.0)
Proceeds from borrowings under short-term debt facilities		0.0	0.0
Repayments of borrowings under short-term debt facilities		0.0	0.0
Payments of deferred financing costs		(8.6)	(0.1)
Proceeds from shares issued under the ATM Program		0.0
Taxes withheld for stock-based compensation		0.0	0.0
Dividends		0.0	0.0
Intercompany		(166.8)	(14.3)
Net cash flow provided by (used for) financing activities		474.6	54.6
Effect of exchange rate changes on cash, cash equivalents and restricted cash		0.0	0.0
Net increase (decrease) in cash, cash equivalents and restricted cash		416.0	(1.0)
Cash, cash equivalents and restricted cash, beginning of period		12.0	10.2
Cash, cash equivalents and restricted cash, end of period	9.2	428.0	9.2
Guarantor Subsidiaries
Condensed Statements of Cash Flows, Captions [Line Items]
Net cash flow provided by (used for) operating activities		133.2	130.6
Capital expenditures		(35.5)	(39.7)
Acquisitions		(34.4)	(4.3)
MTA franchise rights		(10.7)	(6.1)
Net proceeds from dispositions		2.2	3.4
Net cash flow provided by (used for) investing activities		(78.4)	(46.7)
Proceeds from long-term debt borrowings		0.0	0.0
Repayments of long-term debt borrowings		0.0	0.0
Proceeds from borrowings under short-term debt facilities		0.0	0.0
Repayments of borrowings under short-term debt facilities		(75.0)	0.0
Payments of deferred financing costs		0.0	0.0
Proceeds from shares issued under the ATM Program		0.0
Taxes withheld for stock-based compensation		(7.7)	(8.1)
Dividends		0.0	0.0
Intercompany		29.6	(74.0)
Net cash flow provided by (used for) financing activities		(53.1)	(82.1)
Effect of exchange rate changes on cash, cash equivalents and restricted cash		0.0	0.0
Net increase (decrease) in cash, cash equivalents and restricted cash		1.7	1.8
Cash, cash equivalents and restricted cash, beginning of period		1.4	3.7
Cash, cash equivalents and restricted cash, end of period	5.5	3.1	5.5
Non-Guarantor Subsidiaries
Condensed Statements of Cash Flows, Captions [Line Items]
Net cash flow provided by (used for) operating activities		9.7	(6.0)
Capital expenditures		(4.1)	(6.7)
Acquisitions		0.0	0.0
MTA franchise rights		0.0	0.0
Net proceeds from dispositions		0.0	0.0
Net cash flow provided by (used for) investing activities		(4.1)	(6.7)
Proceeds from long-term debt borrowings		0.0	0.0
Repayments of long-term debt borrowings		0.0	0.0
Proceeds from borrowings under short-term debt facilities		30.0	75.0
Repayments of borrowings under short-term debt facilities		(115.0)	(55.0)
Payments of deferred financing costs		0.0	0.0
Proceeds from shares issued under the ATM Program		0.0
Taxes withheld for stock-based compensation		0.0	0.0
Dividends		(1.1)	(1.4)
Intercompany		84.5	(13.1)
Net cash flow provided by (used for) financing activities		(1.6)	5.5
Effect of exchange rate changes on cash, cash equivalents and restricted cash		0.4	(0.2)
Net increase (decrease) in cash, cash equivalents and restricted cash		4.4	(7.4)
Cash, cash equivalents and restricted cash, beginning of period		40.7	34.4
Cash, cash equivalents and restricted cash, end of period	$ 27.0	$ 45.1	$ 27.0

The net change during the reporting period in intercompany amounts.

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Purchase Of MTA Franchise Rights

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