Consolidated Statements of Comprehensive Income - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Net income (loss)	$ 102.1	$ 353.7	$ 75.6
Other comprehensive income (loss), net of tax:
Unrealized gains on CyrusOne, net of tax of $36.9	68.1	0.0	0.0
Foreign currency translation loss	(0.1)	(0.4)	(0.1)
Defined benefit plans:
Net gain (loss) arising from remeasurement during the period, net of tax of $3.6, ($3.4), ($25.0)	6.6	(6.6)	(45.4)
Amortization of prior service benefits included in net income, net of tax of ($5.2), ($5.5), ($5.4)	(9.4)	(9.8)	(9.8)
Amortization of net actuarial loss included in net income, net of tax of $8.5, $10.8, $8.0	15.5	19.5	14.7
Reclassification adjustment for curtailment loss included in net income, net of tax of $0.1	0.0	0.2	0.0
Total other comprehensive income (loss), net of tax	80.7	2.9	(40.6)
Total comprehensive income	$ 182.8	$ 356.6	$ 35.0