Earnings Per Share and Equity - Narrative (Details) - USD ($) $ in Millions	1 Months Ended	3 Months Ended		9 Months Ended
	Jun. 30, 2017	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016	Jun. 01, 2017	Dec. 31, 2016
Statement Of Equity Line Item [Line Items]
Treasury Stock, Shares		1,832,457		1,832,457			34,743,157
Treasury Stock, Value		$ 123		$ 123		$ 2,300	$ 2,327
Equity units issued [Member]
Statement Of Equity Line Item [Line Items]
Stock options not included in the calculation of diluted common shares outstanding			1,000,000
Stock Issued During Period, Shares, Treasury Stock Reissued	33,000,000
Treasury Stock, Shares						35,000,000
Employee Stock Option [Member]
Statement Of Equity Line Item [Line Items]
Stock options not included in the calculation of diluted common shares outstanding		7,000,000	11,000,000	9,000,000	12,000,000