Condensed Consolidating Financial Information (Condensed Consolidating Statements of Cash Flows) (Details) - USD ($) $ in Millions	1 Months Ended	12 Months Ended
	Jan. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Condensed Cash Flow Statements, Captions [Line Items]
Net cash provided by (used in) operating activities		$ 964	$ 1,223	$ 1,097
Investing activities:
Capital investments		(1,099)	(1,290)	(1,268)
Proceeds from sale of property and equipment		54	1,643	10
Other		0	6	6
Net cash provided by (used in) investing activities		(1,045)	359	(1,252)
Financing activities
Intercompany activities		0	0	0
Payments on current portion of long-term debt		(52)	0	(328)
Payments on long-term debt		(54)	(2,095)	(1,139)
Payments on revolving credit facility		(532)	(1,983)	0
Borrowings under revolving credit facility		566	1,983	0
Change in bank drafts outstanding		(19)	17	9
Debt issuance costs		(3)	(9)	(24)
Proceeds from issuance of long-term debt		0	0	1,150
Purchase of treasury stock		(21)	(180)	0
Cash paid for tax withholding		(1)	(3)	(2)
Preferred stock dividend	$ (27)	0	(27)	(16)
Other		1	0	(2)
Net cash used in financing activities		(115)	(2,297)	(352)
Decrease in cash and cash equivalents		(196)	(715)	(507)
Cash and cash equivalents at beginning of year	916	201	916	1,423
Cash and cash equivalents at end of year		5	201	916
Reportable Legal Entities | Parent
Condensed Cash Flow Statements, Captions [Line Items]
Net cash provided by (used in) operating activities		1,280	304	1,019
Investing activities:
Capital investments		(4)	(20)	(13)
Proceeds from sale of property and equipment		0	0	1
Other			0	1
Net cash provided by (used in) investing activities		(4)	(20)	(11)
Financing activities
Intercompany activities		(1,357)	1,300	(1,158)
Payments on current portion of long-term debt		(52)		(328)
Payments on long-term debt		(54)	(2,095)	(1,139)
Payments on revolving credit facility		(532)	(1,983)
Borrowings under revolving credit facility		566	1,983
Change in bank drafts outstanding		(19)	17	9
Debt issuance costs		(3)	(9)	(24)
Proceeds from issuance of long-term debt				1,150
Purchase of treasury stock		(21)	(180)
Cash paid for tax withholding		(1)	(3)	(2)
Preferred stock dividend			(27)	(16)
Other		1		(2)
Net cash used in financing activities		(1,472)	(997)	(1,510)
Decrease in cash and cash equivalents		(196)	(713)	(502)
Cash and cash equivalents at beginning of year	914	201	914	1,416
Cash and cash equivalents at end of year		5	201	914
Reportable Legal Entities | Guarantors
Condensed Cash Flow Statements, Captions [Line Items]
Net cash provided by (used in) operating activities		629	1,595	1,327
Investing activities:
Capital investments		(1,093)	(1,270)	(1,250)
Proceeds from sale of property and equipment		54	1,643	9
Other			6	5
Net cash provided by (used in) investing activities		(1,039)	379	(1,236)
Financing activities
Intercompany activities		410	(1,976)	(96)
Payments on current portion of long-term debt		0		0
Payments on long-term debt		0	0	0
Payments on revolving credit facility		0	0
Borrowings under revolving credit facility		0	0
Change in bank drafts outstanding		0	0	0
Debt issuance costs		0	0	0
Proceeds from issuance of long-term debt				0
Purchase of treasury stock		0	0
Cash paid for tax withholding		0	0	0
Preferred stock dividend			0	0
Other		0		0
Net cash used in financing activities		410	(1,976)	(96)
Decrease in cash and cash equivalents		0	(2)	(5)
Cash and cash equivalents at beginning of year	2	0	2	7
Cash and cash equivalents at end of year		0	0	2
Reportable Legal Entities | Non-Guarantors
Condensed Cash Flow Statements, Captions [Line Items]
Net cash provided by (used in) operating activities		0	0	0
Investing activities:
Capital investments		(2)	0	(5)
Proceeds from sale of property and equipment		0	0	0
Other			0	0
Net cash provided by (used in) investing activities		(2)	0	(5)
Financing activities
Intercompany activities		2	0	5
Payments on current portion of long-term debt		0		0
Payments on long-term debt		0	0	0
Payments on revolving credit facility		0	0
Borrowings under revolving credit facility		0	0
Change in bank drafts outstanding		0	0	0
Debt issuance costs		0	0	0
Proceeds from issuance of long-term debt				0
Purchase of treasury stock		0	0
Cash paid for tax withholding		0	0	0
Preferred stock dividend			0	0
Other		0		0
Net cash used in financing activities		2	0	5
Decrease in cash and cash equivalents		0	0	0
Cash and cash equivalents at beginning of year	0	0	0	0
Cash and cash equivalents at end of year		0	0	0
Eliminations
Condensed Cash Flow Statements, Captions [Line Items]
Net cash provided by (used in) operating activities		(945)	(676)	(1,249)
Investing activities:
Capital investments		0	0	0
Proceeds from sale of property and equipment		0	0	0
Other			0	0
Net cash provided by (used in) investing activities		0	0	0
Financing activities
Intercompany activities		945	676	1,249
Payments on current portion of long-term debt		0		0
Payments on long-term debt		0	0	0
Payments on revolving credit facility		0	0
Borrowings under revolving credit facility		0	0
Change in bank drafts outstanding		0	0	0
Debt issuance costs		0	0	0
Proceeds from issuance of long-term debt				0
Purchase of treasury stock		0	0
Cash paid for tax withholding		0	0	0
Preferred stock dividend			0	0
Other		0		0
Net cash used in financing activities		945	676	1,249
Decrease in cash and cash equivalents		0	0	0
Cash and cash equivalents at beginning of year	$ 0	0	0	0
Cash and cash equivalents at end of year		$ 0	$ 0	$ 0