Earnings Per Share and Equity - Narrative (Details) - USD ($) $ in Millions	1 Months Ended	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016	Jun. 01, 2017	Mar. 31, 2017	Dec. 31, 2016
Statement Of Equity Line Item [Line Items]
Treasury Stock, Value	$ (123)	$ (123)		$ (123)		$ (2,300)	$ 123	$ (2,327)
Treasury Stock, Shares	1,832,457	1,832,457		1,832,457				34,743,157
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		2,000,000
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		8,000,000	11,000,000	9,000,000	12,000,000