Equity (Common Stock - Narrative) (Details) - USD ($) $ in Millions	3 Months Ended				6 Months Ended
	Jun. 30, 2019	Mar. 31, 2019	Jun. 30, 2018	Mar. 31, 2018	Jun. 30, 2019	Jun. 30, 2018
Equity [Abstract]
Treasury Stock, Shares, Acquired					26,954,935	45,540,491
Treasury Stock, Value, Acquired, Cost Method	$ 750	$ 500	$ 1,115	$ 1,041	$ 1,300	$ 2,200