Condensed Consolidating Financial Information (Condensed Consolidating Statements of Cash Flows) (Details) - USD ($) $ in Millions	6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018
Condensed Cash Flow Statements, Captions [Line Items]
Net cash provided by (used in) operating activities	$ 543	$ 664
Investing activities:
Capital investments	(586)	(684)
Proceeds from sale	26	6
Other		9
Net cash used in investing activities	(560)	(675)
Financing activities:
Intercompany activities	0	0
Change in bank drafts outstanding	(7)	0
Purchase of treasury stock	(21)	0
Cash paid for tax withholding	(1)	(1)
Payments on long-term debt	0	(1,191)
Payments on revolving credit facility	0	(645)
Borrowings under revolving credit facility	0	1,005
Preferred stock dividend	0	(27)
Other		(10)
Net cash used in financing activities	(29)	(868)
Decrease in cash and cash equivalents	(46)	(879)
Cash and cash equivalents at beginning of year	201	916
Cash and cash equivalents at end of period	155	37
Parent
Condensed Cash Flow Statements, Captions [Line Items]
Net cash provided by (used in) operating activities	1,124	276
Investing activities:
Capital investments	(1)	(6)
Proceeds from sale	0
Other		0
Net cash used in investing activities	(1)	(6)
Financing activities:
Intercompany activities	(1,140)	(287)
Change in bank drafts outstanding	(7)
Purchase of treasury stock	(21)
Cash paid for tax withholding	(1)
Payments on long-term debt		(1,191)
Payments on revolving credit facility		(645)
Borrowings under revolving credit facility		1,005
Preferred stock dividend		(27)
Other		(10)
Net cash used in financing activities	(1,169)	(1,155)
Decrease in cash and cash equivalents	(46)	(885)
Cash and cash equivalents at beginning of year	201	914
Cash and cash equivalents at end of period	155	29
Guarantors
Condensed Cash Flow Statements, Captions [Line Items]
Net cash provided by (used in) operating activities	179	725
Investing activities:
Capital investments	(584)	(678)
Proceeds from sale	26
Other		9
Net cash used in investing activities	(558)	(669)
Financing activities:
Intercompany activities	379	(50)
Change in bank drafts outstanding	0
Purchase of treasury stock	0
Cash paid for tax withholding	0
Payments on long-term debt		0
Payments on revolving credit facility		0
Borrowings under revolving credit facility		0
Preferred stock dividend		0
Other		0
Net cash used in financing activities	379	(50)
Decrease in cash and cash equivalents	0	6
Cash and cash equivalents at beginning of year	0	2
Cash and cash equivalents at end of period	0	8
Non-Guarantors
Condensed Cash Flow Statements, Captions [Line Items]
Net cash provided by (used in) operating activities	0	0
Investing activities:
Capital investments	(1)	0
Proceeds from sale	0
Other		0
Net cash used in investing activities	(1)	0
Financing activities:
Intercompany activities	1	0
Change in bank drafts outstanding	0
Purchase of treasury stock	0
Cash paid for tax withholding	0
Payments on long-term debt		0
Payments on revolving credit facility		0
Borrowings under revolving credit facility		0
Preferred stock dividend		0
Other		0
Net cash used in financing activities	1	0
Decrease in cash and cash equivalents	0	0
Cash and cash equivalents at beginning of year	0	0
Cash and cash equivalents at end of period	0	0
Eliminations
Condensed Cash Flow Statements, Captions [Line Items]
Net cash provided by (used in) operating activities	(760)	(337)
Investing activities:
Capital investments	0	0
Proceeds from sale	0
Other		0
Net cash used in investing activities	0	0
Financing activities:
Intercompany activities	760	337
Change in bank drafts outstanding	0
Purchase of treasury stock	0
Cash paid for tax withholding	0
Payments on long-term debt		0
Payments on revolving credit facility		0
Borrowings under revolving credit facility		0
Preferred stock dividend		0
Other		0
Net cash used in financing activities	760	337
Decrease in cash and cash equivalents	0	0
Cash and cash equivalents at beginning of year	0	0
Cash and cash equivalents at end of period	$ 0	$ 0