Subsequent Event (Details) - USD ($) $ / shares in Units, $ in Millions	1 Months Ended	3 Months Ended			6 Months Ended
	Jul. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016	Dec. 31, 2016
Subsequent Event [Line Items]
Treasury Stock, Shares, Acquired					34,354,967	1,445,864
Treasury Stock, Value, Acquired, Cost Method					$ 1,810	$ 70
Secured Debt			$ 1,235		1,235		$ 4,071
Other			$ 810	$ 516	$ 1,251	$ 989
Subsequent Event [Member]
Subsequent Event [Line Items]
Treasury Stock, Shares, Acquired	892,524
Treasury Stock, Value, Acquired, Cost Method	$ 49
Approved dividend, amount per share		$ 0.40
Estimated aggregate dividend payment		$ 426