Short-term Borrowings and Other Debt Obligations (Narrative) (Details)		3 Months Ended			9 Months Ended
	Feb. 28, 2018 USD ($)	Dec. 31, 2018 USD ($)	Sep. 30, 2018 USD ($)	Sep. 30, 2017 USD ($)	Sep. 30, 2018 USD ($)	Sep. 30, 2017 USD ($)	Mar. 31, 2018
Short-term Debt [Line Items]
Credit agreement, maximum capacity			$ 1,238,000,000		$ 1,238,000,000
Remaining borrowing capacity			378,000,000		$ 378,000,000
Line of Credit Facility, Collateral					93
Debt instrument, covenant, senior leverage ratio, period two					2.5
Debt instrument, covenant, specified leverage and letter of credit ratio, period two					3.5
Debt instrument, covenant, asset coverage ratio					4.0
Debt Instrument, Covenant, Initial Current Asset Coverage Ratio					1.5
Debt Instrument, Covenant, Secondary Current Asset Coverage Ratio					2.1
Bond Tender and Call Premium			0	$ 0	$ (34,000,000)	$ 0
Borrowings of Long-term Debt					586,000,000	250,000,000
Performance bonds			9,000,000		9,000,000
Repayments of Long-term Debt, Long-term Capital Lease Obligations, and Capital Securities					471,000,000	$ 53,000,000
364 Day Secured RCF [Member]
Short-term Debt [Line Items]
Short-term debt			317,000,000		317,000,000
Revolving Credit Facility
Short-term Debt [Line Items]
Short-term debt			583,000,000		583,000,000
Committed letters of credit
Short-term Debt [Line Items]
Letters of Credit Outstanding, Amount			326,000,000		326,000,000
Domestic and foreign facility
Short-term Debt [Line Items]
Short term borrowings			18,000,000		18,000,000
Committed Letters of Credit [Member]
Short-term Debt [Line Items]
Letters of Credit Outstanding, Amount			205,000,000		205,000,000
A&R Credit Agreement
Short-term Debt [Line Items]
Credit agreement, maximum capacity			900,000,000		900,000,000
Senior Notes, 9.875 Percent due 2025
Short-term Debt [Line Items]
Long-term Debt	$ 600,000,000
Senior Notes, 9.625% due 2019
Short-term Debt [Line Items]
Long-term Debt	425,000,000
Interest Payable	20,000,000
Repayments of Long-term Debt, Long-term Capital Lease Obligations, and Capital Securities	$ 475,000,000
Term Loan Borrowings before Debt Issuance Cost [Member]
Short-term Debt [Line Items]
Debt and Capital Lease Obligations			338,000,000		338,000,000
Senior Notes | Senior Notes, 9.875 Percent due 2025
Short-term Debt [Line Items]
Stated interest rate on debt	9.875%
Senior Notes | Senior Notes, 9.625% due 2019
Short-term Debt [Line Items]
Stated interest rate on debt	9.625%
Senior Notes | Senior Notes, 6.00% due 2018
Short-term Debt [Line Items]
Stated interest rate on debt							6.00%
Extending Lenders | Amended Credit Agreement [Member]
Short-term Debt [Line Items]
Credit agreement, maximum capacity			357,000,000		357,000,000
Nonextending Lenders [Member] | Amended Credit Agreement [Member]
Short-term Debt [Line Items]
Credit agreement, maximum capacity			$ 226,000,000		$ 226,000,000
London Interbank Offered Rate (LIBOR) | Term Loan Agreement
Short-term Debt [Line Items]
Basis spread on variable rate (as a percent)			2.30%
London Interbank Offered Rate (LIBOR) | 364-day credit agreement [Member]
Short-term Debt [Line Items]
Basis spread on variable rate (as a percent)			3.05%
London Interbank Offered Rate (LIBOR) | Extending Lenders | Minimum | A&R Credit Agreement
Short-term Debt [Line Items]
Basis spread on variable rate (as a percent)			3.55%
London Interbank Offered Rate (LIBOR) | Nonextending Lenders [Member] | Minimum | A&R Credit Agreement
Short-term Debt [Line Items]
Basis spread on variable rate (as a percent)			2.80%
Forecast
Short-term Debt [Line Items]
Line of Credit Facility Reduction in Borrowing Capacity		$ 54,000,000