Income Taxes (Unrecognized Tax Benefits And Associated Interest And Penalties) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Unrecognized Tax Benefits [Roll Forward]
Unrecognized tax benefits, beginning balance	$ 16.6	$ 0.0
Additions for tax positions related to prior years		0.0
Reductions for tax positions related to prior years	(13.6)
Additions for tax positions related to current year	43.3	16.6
Reductions for tax positions due to settlements	(0.2)	0.0
Additions for tax positions related to purchase accounting	50.2
Unrecognized tax benefits, ending balance	96.3	16.6
Federal, State and Foreign Tax
Unrecognized Tax Benefits [Roll Forward]
Unrecognized tax benefits, beginning balance	16.6	0.0
Additions for tax positions related to prior years		0.0
Reductions for tax positions related to prior years	(13.6)
Additions for tax positions related to current year	39.5	16.6
Reductions for tax positions due to settlements	(0.2)	0.0
Additions for tax positions related to purchase accounting	48.1
Unrecognized tax benefits, ending balance	90.4	16.6
Accrued Interest and Penalties
Unrecognized Tax Benefits [Roll Forward]
Unrecognized tax benefits, beginning balance	0.0	0.0
Additions for tax positions related to prior years		0.0
Reductions for tax positions related to prior years	0.0
Additions for tax positions related to current year	3.8	0.0
Reductions for tax positions due to settlements	0.0	0.0
Additions for tax positions related to purchase accounting	2.1
Unrecognized tax benefits, ending balance	$ 5.9	$ 0.0