Capital Stock (Schedule of Common Stock) (Details) - shares	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Capital Stock [Roll Forward]
Shares issued, beginning of period (in shares)	2,109,316,331
Shares repurchased, beginning of period (in shares)	(557,930,784)
Shares issued, end of period (in shares)	2,109,316,331	2,109,316,331
Shares repurchased, end of period (in shares)	(556,098,569)	(557,930,784)
Shares Issued [Member]
Capital Stock [Roll Forward]
Shares issued, beginning of period (in shares)	2,109,316,331	2,109,316,331	2,109,316,331
Shares issued, end of period (in shares)	2,109,316,331	2,109,316,331	2,109,316,331
Shares Repurchased [Member]
Capital Stock [Roll Forward]
Shares repurchased, beginning of period (in shares)	(557,930,784)	(559,972,262)	(562,416,635)
Issuance of stock awards and exercise of stock options (in shares)	1,832,215	2,041,478	2,444,373
Shares repurchased, end of period (in shares)	(556,098,569)	(557,930,784)	(559,972,262)
Shares Outstanding [Member]
Capital Stock [Roll Forward]
Shares outstanding, beginning of period (in shares)	1,551,385,547	1,549,344,069	1,546,899,696
Issuance of stock awards and exercise of stock options (in shares)	1,832,215	2,041,478	2,444,373
Shares outstanding, end of period (in shares)	1,553,217,762	1,551,385,547	1,549,344,069