Income Taxes (Summary Of Significant Components Of Deferred Income Tax Assets (Liabilities)) (Details) - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017
Effective Income Tax Rate Reconciliation, Amount [Abstract]
Net operating loss carryforwards	$ 148.4	$ 187.1
Foreign tax credits	123.6	132.3
Interest limitation carryforwards	40.2	0.0
Premiums on long-term debt	23.8	36.1
Employee benefits, including share-based compensation	15.4	20.7
Deferred revenue	10.3	26.0
Other	14.5	12.8
Total deferred tax assets	376.2	415.0
Valuation allowance	(316.0)	(278.8)
Net deferred tax assets	60.2	136.2
Property and equipment	(54.5)	(51.5)
Deferred U.S. tax on foreign income	(31.5)	(24.8)
Deferred costs	(5.3)	(9.1)
Deferred transition tax	0.0	(13.7)
Other	(3.7)	(8.7)
Total deferred tax liabilities	95.0	107.8
Total deferred tax liabilities	$ (34.8)
Net deferred tax asset (liability)		$ 28.4