Income Taxes (Schedule of Components of Deferred Income Taxes) (Details) - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017
Assets
Net operating loss and credit carryforwards	$ 743	$ 583
Self-insurance liabilities	69	78
Long-term debt and interest	84	6
Accounts receivable	58	144
Section 163(j) interest limitation	144
Accrued vacation	26	27
Other comprehensive income	4	9
Stock-based compensation	4	10
Deferred compensation	64	77
Other	15	89
Total Deferred Income Tax Assets, Gross	1,211	1,023
Valuation Allowance	(701)	(489)
Total Deferred Income Tax Assets, Net	510	534
Liabilities
Property and equipment	237	263
Prepaid expenses	27	30
Intangibles	134	128
Investments in unconsolidated affiliates	55	54
Other liabilities	14	16
Total Deferred Income Tax Liabilities, Gross	$ 467	$ 491