Equity (Changes in Common Stock) (Details) - shares	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Class A Common Stock [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Common stock, shares outstanding at beginning of period (in shares)	4,635,063,642	4,742,000,000	4,875,000,000
Stock compensation plans (in shares)	15,000,000	19,000,000	23,000,000
Repurchases and retirements of common stock (in shares)	(140,000,000)	(131,000,000)	(161,000,000)
Employee stock purchase plan (in shares)	7,000,000	5,000,000	5,000,000
Common stock, shares outstanding at end of period (in shares)	4,516,518,147	4,635,063,642	4,742,000,000
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
Common stock, shares outstanding at end of period (in shares)	9,444,375	9,444,375	9,000,000