Subsequent Events Subsequent Events (Common Stock Repurchases) (Details) - USD ($) $ in Millions	2 Months Ended	12 Months Ended
	Feb. 16, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Subsequent Event [Line Items]
Treasury Stock, Shares, Acquired		56,599,540	6,948,739	39,491,991
Treasury Stock, Value, Acquired, Cost Method		$ 2,927	$ 372	$ 1,930
Subsequent Event [Member]
Subsequent Event [Line Items]
Treasury Stock, Shares, Acquired	7,499,116
Treasury Stock, Value, Acquired, Cost Method	$ 392