Accumulated Other Comprehensive Loss (Components Of Accumulated Other Comprehensive Loss) (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other Comprehensive Income (Loss), before Reclassifications, Net of Tax		$ 7.6	$ (16.5)	$ (9.6)
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax		2.4	5.5	2.6
Net current-period other comprehensive income (loss)		10.0	(11.0)	(7.0)
Allocation of AOCI to Noncontrolling Interest	[1]		2.0
Distribution of CPG to shareholders			24.5
Accumulated other comprehensive loss		(25.1)	(35.1)	(50.6)	$ (43.6)
Gains and Losses on Securities
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other Comprehensive Income (Loss), before Reclassifications, Net of Tax		0.0	(0.5)	0.9
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax		(0.1)	(0.3)	(0.3)
Net current-period other comprehensive income (loss)		(0.1)	(0.8)	0.6
Allocation of AOCI to Noncontrolling Interest			0.0
Distribution of CPG to shareholders			0.0
Accumulated other comprehensive loss		(0.6)	(0.5)	0.3	(0.3)
Gains and Losses on Cash Flow Hedges
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other Comprehensive Income (Loss), before Reclassifications, Net of Tax		7.1	(11.0)	(0.3)
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax		1.5	3.2	2.5
Net current-period other comprehensive income (loss)		8.6	(7.8)	2.2
Allocation of AOCI to Noncontrolling Interest			2.0
Distribution of CPG to shareholders			13.9
Accumulated other comprehensive loss		(6.9)	(15.5)	(23.6)	(25.8)
Pension and OPEB Items
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other Comprehensive Income (Loss), before Reclassifications, Net of Tax		0.5	(5.0)	(10.2)
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax		1.0	2.6	0.4
Net current-period other comprehensive income (loss)		1.5	(2.4)	(9.8)
Allocation of AOCI to Noncontrolling Interest			0.0
Distribution of CPG to shareholders			10.6
Accumulated other comprehensive loss		$ (17.6)	$ (19.1)	$ (27.3)	$ (17.5)

[1] This transaction, which occurred prior to the Separation, was distributed through retained earnings as part of the Separation on July 1, 2015.