Share-Based Compensation (Stock Option and SAR Activity) (Details) $ / shares in Units, shares in Millions, $ in Millions	12 Months Ended
	Dec. 31, 2017 USD ($) $ / shares shares
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward]
Outstanding at the beginning of the period | shares	36
Granted, Shares | shares	15
Exercised, Shares | shares	(12)
Forfeitures, Shares | shares	(2)
Outstanding at the end of the period | shares	37
Exercisable at end of period, Shares | shares	16
Vested and expected to vest end of period, Shares | shares	36
Outstanding at beginning of period, Weighted-Average Exercise Price | $ / shares	$ 84
Granted, Weighted-Average Exercise Price | $ / shares	111
Exercised, Weighted-Average Exercise Price | $ / shares	55
Forfeitures, Weighted Average Exercise Price | $ / shares	125
Outstanding at end of period, Weighted-Average Exercise Price | $ / shares	102
Exercisable at end of period, Weighted-Average Exercise Price | $ / shares	67
Vested and expected to vest end of period, Weighted-Average Exercise Price | $ / shares	$ 101
Outstanding at end of period, Weighted Average Remaining Contractual Term (in years)	6 years 7 months 6 days
Exercisable at end of period, Weighted Average Remaining Contractual Term (in years)	4 years 9 months 18 days
Vested and expected to vest end of period, Weighted Average Remaining Contractual Term (in years)	6 years 7 months 6 days
Outstanding at end of period, Aggregate Intrinsic Value | $	$ 4,443
Exercisable at end of period, Aggregate Intrinsic Value | $	2,412
Vested and expected to vest end of period, Aggregate Intrinsic Value | $	$ 4,363