Statements Of Consolidated Common Stockholders' Equity - USD ($) $ in Millions		Total	Common Stock	Treasury Stock	Additional Paid-in Capital	Retained Deficit	Accumulated Other Comprehensive Loss
Beginning Balance at Dec. 31, 2013		$ 5,886.6	$ 3.2	$ (48.6)	$ 4,690.1	$ 1,285.5	$ (43.6)
Comprehensive Income (Loss):
Net Income		530.0	0.0	0.0	0.0	530.0	0.0
Other comprehensive loss, net of tax		(7.0)	0.0	0.0	0.0	0.0	(7.0)
Dividends:
Common stock		(321.5)	0.0	0.0	0.0	(321.5)	0.0
Treasury stock acquired		(10.3)	0.0	(10.3)	0.0	0.0	0.0
Stock issuances:
Employee stock purchase plan		4.2	0.0	0.0	4.2	0.0	0.0
Long-term incentive plan		40.2	0.0	0.0	40.2	0.0	0.0
401(k) and profit sharing		45.3	0.0	0.0	45.3	0.0	0.0
Dividend reinvestment plan		7.8	0.0	0.0	7.8	0.0	0.0
Ending Balance at Dec. 31, 2014		6,175.3	3.2	(58.9)	4,787.6	1,494.0	(50.6)
Comprehensive Income (Loss):
Net Income		286.5	0.0	0.0	0.0	286.5	0.0
Other comprehensive loss, net of tax		(11.0)	0.0	0.0	0.0	0.0	(11.0)
Allocation of AOCI to Noncontrolling Interest	[1]	2.0	0.0	0.0	0.0	0.0	2.0
Sale of interest in Columbia OpCo to CPPL	[1],[2]	227.1	0.0	0.0	227.1	0.0	0.0
Dividends:
Common stock		(263.5)	0.0	0.0	0.0	(263.5)	0.0
Distribution of CPG stock to shareholders		(2,615.8)	0.0	0.0	0.0	(2,640.3)	24.5
Treasury stock acquired		(20.4)	0.0	(20.4)	0.0	0.0	0.0
Stock issuances:
Employee stock purchase plan		5.1	0.0	0.0	5.1	0.0	0.0
Long-term incentive plan		4.2	0.0	0.0	4.2	0.0	0.0
401(k) and profit sharing		46.7	0.0	0.0	46.7	0.0	0.0
Dividend reinvestment plan		7.3	0.0	0.0	7.3	0.0	0.0
Ending Balance at Dec. 31, 2015		3,843.5	3.2	(79.3)	5,078.0	(1,123.3)	(35.1)
Dividends:
Cumulative effect of change in accounting principle		25.3	0.0	0.0	0.0	25.3	0.0
Net Income		331.5	0.0	0.0	0.0	331.5	0.0
Other comprehensive loss, net of tax		10.0	0.0	0.0	0.0	0.0	10.0
Common stock		(205.7)	0.0	0.0	0.0	(205.7)	0.0
Treasury stock acquired		(9.4)	0.0	(9.4)	0.0	0.0	0.0
Stock issuances:
Common stock		0.1	0.1	0.0	0.0	0.0	0.0
Employee stock purchase plan		4.7	0.0	0.0	4.7	0.0	0.0
Long-term incentive plan		20.9	0.0	0.0	20.9	0.0	0.0
401(k) and profit sharing		41.4	0.0	0.0	41.4	0.0	0.0
Dividend reinvestment plan		8.9	0.0	0.0	8.9	0.0	0.0
Ending Balance at Dec. 31, 2016		$ 4,071.2	$ 3.3	$ (88.7)	$ 5,153.9	$ (972.2)	$ (25.1)

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

[2] Represents the purchase of an additional 8.4% limited partner interest in Columbia OpCo by an affiliate of CPG, recorded at the historical carrying value of Columbia OpCo's net assets after giving effect to the $1,168.4 million equity contribution from CPPL's IPO completed on February 11, 2015.