Earnings Per Share and Equity - Narrative (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016	Dec. 31, 2016
Statement Of Equity Line Item [Line Items]
Treasury Stock, Shares held	34,743,157		34,743,157
Treasury Stock, Value	$ (2,327)		$ (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		4,000,000
Employee Stock Option [Member]
Statement Of Equity Line Item [Line Items]
Stock options not included in the calculation of diluted common shares outstanding	9,000,000	13,000,000