Disclosures About Fair Value Measurements (Carrying Amounts And Fair Values Of The Company's Financial Instruments) (Detail) - USD ($) $ in Millions		Jun. 30, 2017	Dec. 31, 2016
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Derivative instruments, Assets		$ 225	$ 4
Derivative instruments, Liabilities		0	178
Five Point Five Percent Unsecured Senior Notes Due Twenty Twenty Two [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Unsecured senior notes		619	620
Five Point Five Percent Unsecured Senior Notes Due Twenty Twenty Three [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Unsecured senior notes		1,597	1,621
Four Point Three Seven Five Percent Unsecured Senior Notes [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Unsecured senior notes		614	599
Carrying Reported Amount Fair Value Disclosure [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Derivative instruments, Assets		225	4
Derivative instruments, Liabilities		0	178
Carrying Reported Amount Fair Value Disclosure [Member] | Five Point Five Percent Unsecured Senior Notes Due Twenty Twenty Two [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Unsecured senior notes	[1]	594	594
Carrying Reported Amount Fair Value Disclosure [Member] | Five Point Five Percent Unsecured Senior Notes Due Twenty Twenty Three [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Unsecured senior notes	[1]	1,554	1,555
Carrying Reported Amount Fair Value Disclosure [Member] | Four Point Three Seven Five Percent Unsecured Senior Notes [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Unsecured senior notes	[1]	$ 593	$ 592

[1] The carrying value includes associated deferred loan costs and any premium.