Fair Value Measurements (Schedule of Carrying Values and Fair Values of Financial Instruments) (Details) - USD ($) $ in Millions	Mar. 31, 2018	Dec. 31, 2017
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cost investments, carrying amount	$ 165	$ 159
Cost investments, fair value	0	0
Insurance contracts in nonqualified trusts, carrying amount	42	42
Insurance contracts in nonqualified trusts, fair value	42	42
Long-term debt, including current installments of long-term debt, carrying amount	3,424	3,398
Long-term debt, including current installments of long-term debt, fair value	3,504	3,507
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	42	42
Long-term debt, including current installments of long-term debt, fair value	3,310	3,299
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	$ 194	$ 208