Condensed Consolidating Financial Information (Condensed Consolidating Statements of Cash Flows) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Condensed Cash Flow Statements, Captions [Line Items]
Net cash provided by (used in) operating activities	$ 442	$ 364
Investing activities:
Capital investments	(258)	(302)
Other	0	8
Net cash used in investing activities	(258)	(294)
Financing activities
Intercompany activities	0	0
Change in bank drafts outstanding	3	0
Purchase of treasury stock	(21)	0
Preferred stock dividend	0	(27)
Cash paid for tax withholding	(1)	(1)
Net cash used in financing activities	(19)	(28)
Increase in cash and cash equivalents	165	42
Cash and cash equivalents at beginning of year	201	916
Cash and cash equivalents at end of period	366	958
Parent
Condensed Cash Flow Statements, Captions [Line Items]
Net cash provided by (used in) operating activities	1,031	183
Investing activities:
Capital investments	3	(5)
Other	0	0
Net cash used in investing activities	3	(5)
Financing activities
Intercompany activities	(850)	(116)
Change in bank drafts outstanding	3
Purchase of treasury stock	(21)
Preferred stock dividend		(27)
Cash paid for tax withholding	(1)	(1)
Net cash used in financing activities	(869)	(144)
Increase in cash and cash equivalents	165	34
Cash and cash equivalents at beginning of year	201	914
Cash and cash equivalents at end of period	366	948
Guarantors
Condensed Cash Flow Statements, Captions [Line Items]
Net cash provided by (used in) operating activities	19	428
Investing activities:
Capital investments	(261)	(297)
Other	0	8
Net cash used in investing activities	(261)	(289)
Financing activities
Intercompany activities	242	(131)
Change in bank drafts outstanding	0
Purchase of treasury stock	0
Preferred stock dividend		0
Cash paid for tax withholding	0	0
Net cash used in financing activities	242	(131)
Increase in cash and cash equivalents	0	8
Cash and cash equivalents at beginning of year	0	2
Cash and cash equivalents at end of period	0	10
Non-Guarantors
Condensed Cash Flow Statements, Captions [Line Items]
Net cash provided by (used in) operating activities	0	0
Investing activities:
Capital investments	0	0
Other	0	0
Net cash used in investing activities	0	0
Financing activities
Intercompany activities	0	0
Change in bank drafts outstanding	0
Purchase of treasury stock	0
Preferred stock dividend		0
Cash paid for tax withholding	0	0
Net cash used in financing activities	0	0
Increase 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	(608)	(247)
Investing activities:
Capital investments	0	0
Other	0	0
Net cash used in investing activities	0	0
Financing activities
Intercompany activities	608	247
Change in bank drafts outstanding	0
Purchase of treasury stock	0
Preferred stock dividend		0
Cash paid for tax withholding	0	0
Net cash used in financing activities	608	247
Increase 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