Fair Value Measurements (Schedule of Carrying Values and Fair Values of Financial Instruments) (Details) - USD ($) $ in Millions	Sep. 30, 2017	Dec. 31, 2016
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cost investments, carrying amount	$ 159	$ 155
Cost investments, fair value	0	0
Insurance contracts in nonqualified trusts, carrying amount	46	49
Insurance contracts in nonqualified trusts, fair value	46	49
Long-term debt, including current installments of long-term debt, carrying amount	3,031	2,938
Long-term debt, including current installments of long-term debt, fair value	3,146	3,043
Significant Other Observable Inputs (Level 2) [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cost investments, fair value	0	0
Insurance contracts in nonqualified trusts, fair value	46	49
Long-term debt, including current installments of long-term debt, fair value	2,934	2,826
Unobservable Inputs (Level 3) [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cost investments, fair value	0	0
Insurance contracts in nonqualified trusts, fair value	0	0
Long-term debt, including current installments of long-term debt, fair value	$ 212	$ 217