Income Taxes (Narrative) (Details) $ in Millions, $ in Billions	3 Months Ended
	Dec. 31, 2017 USD ($)	Dec. 31, 2018 USD ($)	Aug. 31, 2016 USD ($)	Aug. 31, 2016 MXN ($)
Income Tax Contingency [Line Items]
Basis difference indefintely reinvested	$ 11.4	$ 14.6
Deferred tax liability not recognized, amount of unrecognized deferred tax liability, temporary differences	2.4	3.0
Reasonably possible decrease in gross unrecognized tax benefits, within 12 months		$ 4.1
Effective income tax rate reconciliation, change in enacted tax rate, amount	$ 6.7
Tax Year 2010 | Mexico
Income Tax Contingency [Line Items]
Administrative assessment amount from tax administration service			$ 157.0	$ 3