Income Taxes (Geographic Sources) (Details 1) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Geographic sources of pretax income
United States									$ 1,412	$ 1,710	$ 1,858
Foreign									180	432	689
Income from continuing operations before income tax provision	$ 469	$ 238	$ 410	$ 475	$ 446	$ 463	$ 615	$ 618	$ 1,592	$ 2,142	$ 2,547