Postretirement Benefit Plans - Employer Contributions to VEBA Trust (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014
Employer contributions to defined postretirement benefit plans
Company contributions	$ 10.8	$ 21.1
VEBA [Member]
Employer contributions to defined postretirement benefit plans
Company contributions	0.0	$ 20.0
Defined Benefit Plans, Estimated Future Employer Contributions in Current Fiscal Year	$ 0.0