Capital Stock (Narrative) (Details) - USD ($) $ / shares in Units, shares in Millions		3 Months Ended							9 Months Ended
	Oct. 12, 2017	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Sep. 30, 2017	Sep. 30, 2016	May 12, 2015	Oct. 02, 2014
Option Indexed to Issuer's Equity [Line Items]
Stock Repurchase Program, Remaining Authorized Repurchase Amount			$ 2,540,500,000						$ 2,540,500,000
Stock Repurchased and Retired During Period, Shares									8.7
Dividends Payable, Date Declared			Jul. 25, 2017	Apr. 27, 2017	Feb. 22, 2017	Jul. 26, 2016	Apr. 26, 2016	Feb. 18, 2016
Common Stock, Dividends, Per Share, Declared			$ 0.70			$ 0.65			$ 2.00	$ 1.95
Dividends Payable, Date to be Paid			Sep. 25, 2017	Jun. 23, 2017	Mar. 24, 2017	Sep. 26, 2016	Jun. 24, 2016	Mar. 25, 2016
Dividends Payable, Date of Record			Sep. 08, 2017	Jun. 09, 2017	Mar. 10, 2017	Sep. 09, 2016	Jun. 10, 2016	Mar. 10, 2016
Increase In Stock Repurchase Program Authorization												$ 5,000,000,000
Stock Repurchased and Retired During Period Average Price									$ 186.80
Stock Repurchased and Retired During Period, Value									$ 1,635,400,000
Equity Unit Purchase Agreements [Member]
Option Indexed to Issuer's Equity [Line Items]
Equity Units Issued											25.0
Equity Units, outstanding principal amount			$ 1,000						1,000
Long-term Debt, Gross			$ 1,250,000,000						$ 1,250,000,000
Subsequent Event [Member]
Option Indexed to Issuer's Equity [Line Items]
Stock Repurchase Program, Remaining Authorized Repurchase Amount	$ 2,410,000,000
Stock Repurchased and Retired During Period, Shares	0.7
Dividends Payable, Date Declared		Oct. 24, 2017
Common Stock, Dividends, Per Share, Declared		$ 0.70
Dividends Payable, Date to be Paid		Dec. 21, 2017
Dividends Payable, Date of Record		Dec. 05, 2017
Stock Repurchased and Retired During Period Average Price	$ 191.35
Stock Repurchased and Retired During Period, Value	$ 130,500,000