Subsequent Events (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended	9 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Sep. 30, 2017	Nov. 01, 2018	May 22, 2018	Nov. 01, 2017
Subsequent Event [Line Items]
Stock Repurchase Program, Authorized Amount					$ 1,500	$ 2,000
Treasury Stock, Shares, Acquired		59,602,926	44,737,625
Treasury Stock, Value, Acquired, Cost Method		$ 2,792	$ 2,305
Estimated aggregate dividend payment		$ 1,263	$ 1,295
Subsequent Event [Member]
Subsequent Event [Line Items]
Stock Repurchase Program, Authorized Amount				$ 2,000
Approved dividend, amount per share	$ 0.42
Estimated aggregate dividend payment	$ 416