Savings Plans, Pension Plans and Other Postretirement Employee Benefits (Long-Term Asset Allocation Ranges) (Details)	12 Months Ended
	Dec. 31, 2017
Minimum [Member]
Domestic and international equities	24.00%
Fixed income securities	38.00%
Alternatives, which may include equities and fixed income securities	12.00%
Cash and cash equivalents	0.00%
Maximum [Member]
Domestic and international equities	48.00%
Fixed income securities	58.00%
Alternatives, which may include equities and fixed income securities	18.00%
Cash and cash equivalents	5.00%