Equity (Common Stock - Narrative) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Equity [Abstract]
Treasury Stock, Shares, Acquired	21,405,327	16,038,791
Treasury Stock, Value, Acquired, Cost Method	$ 1,041	$ 858
Stock Repurchase Program, Remaining Authorized Repurchase Amount	$ 720