Subsequent Event (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended			9 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016	Nov. 01, 2017	Dec. 31, 2016
Subsequent Event [Line Items]
Treasury Stock, Shares, Acquired				44,737,625	1,445,864
Treasury Stock, Value, Acquired, Cost Method				$ 2,305	$ 70
Secured Debt		$ 1,220		1,220			$ 1,274
Other		$ 352	$ 336	$ 1,215	$ 1,090
Subsequent Event [Member]
Subsequent Event [Line Items]
Treasury Stock, Shares, Acquired	2,301,205
Treasury Stock, Value, Acquired, Cost Method	$ 121
Stock Repurchase Program, Authorized Amount						$ 2,000
Approved dividend, amount per share	$ 0.40
Estimated aggregate dividend payment	$ 422