Income Taxes, Unrecognized tax benefits (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Taxes
Gross increases in unrecognized tax benefits related to acquisitions		$ 78.7
Reconciliation of the gross amounts of unrecognized tax benefits excluding interest and penalties
Unrecognized tax benefits as of January 1	$ 106.2	29.8	$ 27.7
Gross increases for tax positions in prior periods	32.7	81.9	0.3
Gross increases for tax positions in current period	2.4	7.0	2.1
Settlements	(11.0)	(10.8)
Lapse of statute of limitations	(3.0)	(1.7)	(0.3)
Unrecognized tax benefits at the end of the period	127.3	106.2	29.8
Estimated interest and penalties included in provision for income taxes	3.7	6.5	1.5
Tax-related interest and penalties liability for unrecognized tax benefits	39.3	35.3	$ 6.0
Liability for unrecognized tax benefits, including penalties and interest, which if recognized would impact the effective tax rate	130.1	$ 138.7
Unrecognized tax benefits, anticipated adjustment for changing facts and circumstances, over the next twelve month period	$ 38.4