Accounting for Stock-Based Compensation (Schedule of Share-based Compensation, Stock Options, Activity) (Details) - Employee Stock Option [Member] - USD ($) $ / shares in Units, $ in Millions	3 Months Ended			6 Months Ended
	Jun. 30, 2015	Mar. 31, 2015	Jun. 30, 2014	Jun. 30, 2015
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Beginning Balance, shares	1,500,768	1,953,727		1,953,727
Granted, Shares	0		0
Exercised, Shares	(128,270)	(452,959)
Forfeited and Cancelled, Shares	(1,000)
Ending Balance, shares	1,371,498	1,500,768		1,371,498
Beginning of Period, Weighted Average Exercise Price	$ 31.18	$ 32.94		$ 32.94
Exercised, Weighted Average Exercise Price	34.01	38.77
Forfeited and Cancelled, Weighted Average Exercise Price	32.28
End of Period, Weighted Average Exercise Price	$ 30.92	$ 31.18		$ 30.92
Weighted Average Remaining Contractual Term				4 years 6 months
Aggregate Intrinsic Value	$ 44			$ 44
Exercisable, Shares	1,370,496			1,370,496
Exercisable, Weighted Average Exercise Price	$ 30.92			$ 30.92
Exercisable, Weighted Average Remaining Contractual Term				4 years 6 months
Exercisable, Aggregate Intrinsic Value	$ 44			$ 44