Subsidiary Guarantors (Condensed Consolidating Statement Of Cash Flows) (Detail) - USD ($) $ in Millions	6 Months Ended
Jun. 30, 2017	Jun. 30, 2016
Condensed Financial Statements Captions [Line Items]
Net cash flows provided by (used in) operating activities	$ 805	$ 676
Net cash flows provided by (used in) investing activities	(168)	(412)
Net cash flows provided by (used in) financing activities	(28)	(12)
Net increase (decrease) in cash and cash equivalents	609	252
Cash and cash equivalents at beginning of period	53	229
Cash and cash equivalents at end of period	662	481
Consolidation Eliminations [Member]
Condensed Financial Statements Captions [Line Items]
Net cash flows provided by (used in) operating activities	0	0
Net cash flows provided by (used in) investing activities	0	0
Net cash flows provided by (used in) financing activities	0	0
Net increase (decrease) in cash and cash equivalents	0	0
Cash and cash equivalents at beginning of period	0	0
Cash and cash equivalents at end of period	0	0
Parent Company [Member]
Condensed Financial Statements Captions [Line Items]
Net cash flows provided by (used in) operating activities	28	12
Net cash flows provided by (used in) investing activities	0	0
Net cash flows provided by (used in) financing activities	(28)	(12)
Net increase (decrease) in cash and cash equivalents	0	0
Cash and cash equivalents at beginning of period	0	0
Cash and cash equivalents at end of period	0	0
Guarantor Subsidiaries [Member]
Condensed Financial Statements Captions [Line Items]
Net cash flows provided by (used in) operating activities	777	664
Net cash flows provided by (used in) investing activities	(168)	(412)
Net cash flows provided by (used in) financing activities	0	0
Net increase (decrease) in cash and cash equivalents	609	252
Cash and cash equivalents at beginning of period	53	229
Cash and cash equivalents at end of period	$ 662	$ 481

Amount of currency on hand as well as demand deposits with banks or financial institutions. Includes other kinds of accounts that have the general characteristics of demand deposits. Also includes short-term, highly liquid investments that are both readily convertible to known amounts of cash and so near their maturity that they present insignificant risk of changes in value because of changes in interest rates. Excludes cash and cash equivalents within disposal group and discontinued operation.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Glossary Cash
-URI http://asc.fasb.org/extlink&oid=6506951

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section 45
-Paragraph 1
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=28358313&loc=d3e6676-107765

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
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-URI http://asc.fasb.org/extlink&oid=66902209&loc=d3e3044-108585

Reference 4: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Glossary Cash Equivalents
-URI http://asc.fasb.org/extlink&oid=6507016

Reference 5: http://www.xbrl.org/2003/role/presentationRef
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-Name Accounting Standards Codification
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Amount of increase (decrease) in cash and cash equivalents. Cash and cash equivalents are the amount of currency on hand as well as demand deposits with banks or financial institutions. Includes other kinds of accounts that have the general characteristics of demand deposits. Also includes short-term, highly liquid investments that are both readily convertible to known amounts of cash and so near their maturity that they present insignificant risk of changes in value because of changes in interest rates. Includes effect from exchange rate changes.

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Amount of cash inflow (outflow) of financing activities, excluding discontinued operations. Financing activity cash flows include obtaining resources from owners and providing them with a return on, and a return of, their investment; borrowing money and repaying amounts borrowed, or settling the obligation; and obtaining and paying for other resources obtained from creditors on long-term credit.

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