Benefit Obligations (Schedule of Company Commitments to Fund Benefit Obligations) (Details) $ in Millions	9 Months Ended
	Sep. 30, 2018 USD ($)
Multiemployer Plans, Pension [Member]
Defined Benefit Plan Disclosure [Line Items]
Total contributions year-to-date	$ 6	[1]
Total expected contributions in current fiscal year	8	[1]
Cash Contributions to Defined Benefit Pension Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Total contributions year-to-date	17
Total expected contributions in current fiscal year	23
Other Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Total contributions year-to-date	17
Total expected contributions in current fiscal year	21
Postretirement Benefit Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Total contributions year-to-date	1
Total expected contributions in current fiscal year	$ 5

[1] The Company makes contributions based on specified percentages of employee contributions.