Employee Benefit Plans (Narrative) (Details) $ in Millions	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016 USD ($)	Jun. 30, 2015	Dec. 31, 2015 USD ($)	Feb. 22, 2015 collective_bargaining_agreement
Defined Benefit Plan Disclosure [Line Items]
Actual return for qualified pension plan assets	7.60%	(0.70%)	7.40%	1.90%
Qualified Pension Plans
Defined Benefit Plan Disclosure [Line Items]
Contributions by employer			$ 3.8
Qualified Pension Plans | Pension Plans, Defined Benefit, Represented Employees
Defined Benefit Plan Disclosure [Line Items]
Agreements with labor unions | collective_bargaining_agreement						2
Post-retirement Healthcare Plans
Defined Benefit Plan Disclosure [Line Items]
Contributions by employer			$ 2.6
Post-retirement Healthcare Plans | Continuing OPEB Plan
Defined Benefit Plan Disclosure [Line Items]
Unrecognized prior service credit for represented employees pension plan recorded in AOCI					$ 37.1
Unrecognized prior service credit, amortization period			10 years 9 months 24 days
Amount to be amortized from AOCI in remainder of year					(306.8)
Post-retirement Healthcare Plans | OPEB Plan
Defined Benefit Plan Disclosure [Line Items]
Amount to be amortized from AOCI in remainder of year					$ (81.9)