Equity (Aggregate Share Repurchases) (Details) - USD ($) shares in Millions, $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Equity, Class of Treasury Stock [Line Items]
Cash consideration	$ 5,435	$ 5,352	$ 7,175
New Authorization [Member]
Equity, Class of Treasury Stock [Line Items]
Cash consideration	$ 5,000	$ 5,000	$ 6,750
Shares repurchased (in shares)	131	161	232