Equity (Changes in Common Stock) (Details) - shares	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Class A Common Stock [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Common stock, shares outstanding at beginning of period (in shares)	4,742,159,011	4,875,000,000	4,272,000,000
Stock compensation plans (in shares)	19,000,000	23,000,000	25,000,000
Repurchases and retirements of common stock (in shares)	(131,000,000)	(161,000,000)	(125,000,000)
Employee stock purchase plan (in shares)	5,000,000	5,000,000	5,000,000
Reclassification of Class A Special common stock (in shares)			694,000,000
Other (in shares)			4,000,000
Common stock, shares outstanding at end of period (in shares)	4,635,063,642	4,742,159,011	4,875,000,000
Class A Special Common Stock [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Common stock, shares outstanding at beginning of period (in shares)	0	0	801,000,000
Stock compensation plans (in shares)	0	0	0
Repurchases and retirements of common stock (in shares)	0	0	(107,000,000)
Employee stock purchase plan (in shares)	0	0	0
Reclassification of Class A Special common stock (in shares)			(694,000,000)
Other (in shares)			0
Common stock, shares outstanding at end of period (in shares)	0	0	0
Class B Common Stock [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Common stock, shares outstanding at beginning of period (in shares)	9,444,375	9,000,000	9,000,000
Stock compensation plans (in shares)	0	0	0
Repurchases and retirements of common stock (in shares)	0	0	0
Employee stock purchase plan (in shares)	0	0	0
Reclassification of Class A Special common stock (in shares)			0
Other (in shares)			0
Common stock, shares outstanding at end of period (in shares)	9,444,375	9,444,375	9,000,000