Subsequent Events Subsequent Events (Common Stock Repurchases) (Details) - USD ($) $ in Millions	2 Months Ended	12 Months Ended
	Feb. 14, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Subsequent Event [Line Items]
Treasury Stock, Shares, Acquired		88,029,138	56,599,540	6,948,739
Treasury Stock, Value, Acquired, Cost Method		$ 3,992	$ 2,927	$ 372
Subsequent Event [Member]
Subsequent Event [Line Items]
Treasury Stock, Shares, Acquired	1,947,100
Treasury Stock, Value, Acquired, Cost Method	$ 85