Income Taxes (Geographic Sources) (Details 1) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Geographic sources of pretax income
United States									$ 1,710	$ 1,858	$ 1,640
Foreign									432	689	330
Income from continuing operations before income tax provision	$ 446	$ 463	$ 615	$ 618	$ 558	$ 720	$ 619	$ 650	$ 2,142	$ 2,547	$ 1,970