Capital Stock (Narrative) (Details) - USD ($)	3 Months Ended			12 Months Ended			31 Months Ended
	Sep. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Jan. 31, 2018	May 31, 2018	Jul. 31, 2017	Oct. 31, 2016	Jul. 31, 2015
Class of Stock [Line Items]
Common stock, shares authorized (in shares)				12,000,000,000
Increase in quarterly dividend rate	14.30%	6.10%		21.20%
Cash dividends declared (USD per share)	$ 0.80	$ 0.7	$ 0.66	$ 3.00	$ 2.54	$ 2.35
Annualized dividend rate (USD per share)				$ 3.20
Repurchase of common stock (in shares)				27,878,324	41,604,141	16,221,001
Average price of repurchased shares (USD per share)				$ 60.00	$ 70.10	$ 63.48
Aggregate cost of shares repurchased				$ 1,673,000,000	$ 2,917,000,000	$ 1,030,000,000
July 2015 Share Repurchase Program [Member]
Class of Stock [Line Items]
Stock repurchase program, authorized amount									$ 4,000,000,000	$ 3,000,000,000	$ 1,000,000,000
Repurchase of common stock (in shares)				300,000	41,600,000	16,200,000	58,700,000
Average price of repurchased shares (USD per share)				$ 71.68	$ 70.10	$ 63.48	$ 68.15
Aggregate cost of shares repurchased				$ 18,000,000	$ 2,917,000,000	$ 1,030,000,000
January 2018 Share Repurchase Program [Member]
Class of Stock [Line Items]
Stock repurchase program, authorized amount							$ 1,000,000,000.0	$ 2,000,000,000.0
Repurchase of common stock (in shares)				27,600,000
Average price of repurchased shares (USD per share)				$ 59.89
Aggregate cost of shares repurchased				$ 1,655,000,000
Amount remaining in the share repurchased program				$ 345,000,000
Serial Preferred Stock [Member]
Class of Stock [Line Items]
Preferred stock, shares authorized (in shares)				10,000,000
Preferred stock, par value (USD per share)				$ 1.00
Preferred stock, shares issued (in shares)				0
Stock Compensation Plan [Member]
Class of Stock [Line Items]
Shares of common stock reserved for stock-based awards (in shares)				40,400,278