Income Taxes (Unrecognized Income Tax Benefits) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns
Balance at January 1	$ 406	$ 416	$ 473
Gross increases for tax positions of prior years	20	80	36
Gross decreases for tax positions of prior years	(104)	(61)	(91)
Gross increases for tax positions of the current year	39	59	87
Settlements	(29)	(63)	(77)
Other	(11)	(25)	(12)
Balance at December 31	$ 321	$ 406	$ 416