Pension Benefits - Weighted Average Asset Allocation for Pension Plans (Details) - Pension Plans, Defined Benefit [Member]	Dec. 31, 2016	Dec. 31, 2015
Defined Benefit Plan Disclosure [Line Items]
Weighted-average asset allocations	100.00%	100.00%
Cash and Short-term Investments [Member]
Defined Benefit Plan Disclosure [Line Items]
Weighted-average asset allocations	2.00%	4.00%
Corporate Bonds and Notes [Member]
Defined Benefit Plan Disclosure [Line Items]
Weighted-average asset allocations	31.00%	28.00%
Common and Preferred Stocks [Member]
Defined Benefit Plan Disclosure [Line Items]
Weighted-average asset allocations	48.00%	43.00%
Exchange Traded Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Weighted-average asset allocations	1.00%	9.00%
Other Assets [Member]
Defined Benefit Plan Disclosure [Line Items]
Weighted-average asset allocations	18.00%	16.00%