Debt, Interest Rate Swap Arrangements (Details) - USD ($) $ in Millions		Jun. 30, 2018	Dec. 31, 2017
Interest Rate Swaps [Member]
Debt Instrument [Line Items]
Notional Amount Of Derivatives		$ 3,100	$ 3,100
Interest Rate Swap, Pay Rate at Period End		4.63%
Cross Currency Interest Rate Contract [Member]
Debt Instrument [Line Items]
Notional Amount Of Derivatives		$ 1,200
Interest Rate Swap, Pay Rate at Period End		1.96%
Senior Notes [Member] | 4.50% Senior Notes Due 2021 [Member] | Interest Rate Swaps [Member]
Debt Instrument [Line Items]
Notional Amount Of Derivatives	[1]	$ 1,000
Interest Rate Swap, Pay Rate Spread above One-month LIBOR		3.442%
Interest Rate Swap, Pay Rate at Period End	[1]	5.4245%
Interest Rate Swap, Fixed Receive Rate		4.50%
Senior Notes [Member] | 3.60% Senior Notes Due 2021 [Member] | Interest Rate Swaps [Member]
Debt Instrument [Line Items]
Notional Amount Of Derivatives		$ 1,100
Interest Rate Swap, Pay Rate Spread above One-month LIBOR		2.515%
Interest Rate Swap, Pay Rate at Period End		4.5883%
Interest Rate Swap, Fixed Receive Rate		3.60%
Senior Notes [Member] | 3.00% Senior Notes Due 2023 [Member] | Interest Rate Swaps [Member]
Debt Instrument [Line Items]
Notional Amount Of Derivatives	[1]	$ 1,000
Interest Rate Swap, Pay Rate Spread above One-month LIBOR		1.764%
Interest Rate Swap, Pay Rate at Period End	[1]	3.8373%
Interest Rate Swap, Fixed Receive Rate		3.00%

[1] The payments on $1.2 billion notional value of these interest rate swaps are offset in part by cross-currency interest rate swaps which effectively reduced the pay rate as of June 30, 2018 from a weighted average of 4.63% to a weighted average of 1.96%.