Equity (Summary of Activity Related to Stock Options) (Details) - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Aug. 07, 2017	Aug. 04, 2017
Aggregate Intrinsic Value
Share Price				$ 48.17	$ 53.92
Stock Options
Shares Under Option
Shares Under Option Outstanding at January 1,	19,482,388
Granted Shares Under Option	709,085
Exercised Shares Under Option	(3,475,198)
Expired Shares Under Option	(2,913,457)
Forfeited Shares Under Option	(115,670)
Other Separation Adjustment Under Option	2,322,606
Shares Under Option Outstanding at December 31,	16,009,754	19,482,388
Vested and expected to vest at December 31,	15,991,119
Shares Under Option Exercisable at December 31,	14,487,455
Weighted Average Exercise Price
Weighted Average Exercise Price Outstanding at January 1,	$ 44.73
Granted Weighted Average Exercise Price	46.85	$ 34.33	$ 45.91
Exercised Weighted Average Exercise Price	33.36
Expired Weighted Average Exercise Price	56.06
Forfeited Weighted Average Exercise Price	40.06
Other Separation Adjustment	38.40
Weighted Average Exercise Price Outstanding at December 31,	38.77	$ 44.73
Weighted Average Exercise Price Aggregate number of stock options expected to vest at December 31,	38.76
Weighted Average Exercise Price Exercisable at December 31,	$ 38.46
Weighted Average Remaining Contractual Term
Weighted Average Remaining Contractual Term Outstanding at January 1,	3 years 6 months 13 days	3 years 8 months 4 days
Weighted Average Remaining Contractual Term Aggregate number of stock options expected to vest at December 31,	3 years 46 days
Weighted Average Remaining Contractual Term Exercisable at December 31,	3 years 6 days
Aggregate Intrinsic Value
Aggregate Intrinsic Value Outstanding at January 1,	$ 218
Aggregate Intrinsic Value Outstanding at December 31,	198	$ 218
Aggregate Intrinsic Value Aggregate number of stock options expected to vest at December 31,	238
Aggregate Intrinsic Value Exercisable at December 31,	$ 185
Sale of Stock, Price Per Share	$ 50.56	$ 48.02