Equity (Common Stock) (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended												12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	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, 2017	Dec. 31, 2016	Dec. 31, 2015
Dividends Payable [Line Items]
Dividend Per Share													$ 1.600	$ 1.575	$ 1.475
Dividend Aggregate													$ 1,717	$ 1,736	$ 1,653
Common stock
Dividends Payable [Line Items]
Declaration Date	Oct. 24, 2017	Jul. 07, 2017	Apr. 25, 2017	Jan. 06, 2017	Oct. 25, 2016	Jul. 07, 2016	Apr. 26, 2016	Jan. 06, 2016	Oct. 27, 2015	Jul. 07, 2015	Apr. 28, 2015	Jan. 06, 2015
Record Date	Nov. 06, 2017	Aug. 07, 2017	May 08, 2017	Feb. 06, 2017	Nov. 07, 2016	Aug. 08, 2016	May 09, 2016	Feb. 05, 2016	Nov. 06, 2015	Aug. 07, 2015	May 11, 2015	Feb. 06, 2015
Payment Date	Dec. 13, 2017	Sep. 13, 2017	Jun. 13, 2017	Mar. 13, 2017	Dec. 13, 2016	Sep. 13, 2016	Jun. 13, 2016	Mar. 14, 2016	Dec. 11, 2015	Sep. 11, 2015	Jun. 12, 2015	Mar. 13, 2015
Dividend Per Share	$ 0.4	$ 0.400	$ 0.400	$ 0.400	$ 0.400	$ 0.400	$ 0.400	$ 0.375	$ 0.375	$ 0.375	$ 0.375	$ 0.350
Dividend Aggregate	$ 422	$ 427	$ 431	$ 437	$ 441	$ 441	$ 441	$ 413	$ 419	$ 420	$ 420	$ 394	$ 1,717	$ 1,736	$ 1,653