Statement of Cash Flows - Derecognition of Right to Use Assets and Right to Use Liabilities (Details) $ in Millions	3 Months Ended			12 Months Ended
	Sep. 30, 2016 USD ($) lease item	Mar. 31, 2016 USD ($) lease	Dec. 31, 2015 USD ($)	Dec. 31, 2016 USD ($) item	Dec. 31, 2015 USD ($) lease	Dec. 31, 2014 USD ($) lease
Right to Use Liabilities
Right to use assets derecognized	$ 4.6	$ 15.4	$ 122.4	$ 20.1	$ 5.4	$ 8.2
Right to use liabilities derecognized	$ 4.7	$ 15.4	$ 127.0	$ 20.0	$ 5.4	$ 8.2
Number of operating leases	1	2		7	2	5
Number of month's rent the lease deposit is less than | item	2