Summary Of Significant Accounting Policies (Narrative) (Detail) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Basis Of Presentation And Significant Accounting Policies [Line Items]
Incremental Common Shares Attributable to Dilutive Effect of Share-based Payment Arrangements	0.3	1.3	0.4	1.2
Income Tax Expense (Benefit)			$ 21
Adjustments related to Income Tax Benefit from Share-Based payment per diluted share			$ 0.09
Excess Tax Benefit from Share-based Compensation, Operating Activities				$ 2
Employee Service Share-based Compensation, Tax Benefit from Compensation Expense			$ 32	$ 12