Fair Value of Financial Instruments (Schedule of Effective Portion of the Pre-tax Loss Reclassified from AOCL into Interest Expense on the Consolidated Statements of Income) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Interest Expense [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Amount of Pre-Tax Loss Reclassified from AOCL into Income (Effective Portion)	$ 5	$ 9