Shareholders' Equity and Dividend Availability Shareholders' Equity and Dividend Availability (Details) - USD ($)	3 Months Ended				12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2018	Dec. 31, 2017	Apr. 30, 2017
Stockholders' Equity Note [Abstract]
Number of authorized shares (in shares)	1,755,000,000.000				1,755,000,000.000
Number of authorized shares, preferred shares (in shares)	5,000,000.0				5,000,000.0
Number of authorized shares, voting common stock (in shares)	1,745,000,000				1,745,000,000
Number of shares authorized, undesignated shares (in shares)	5,000,000				5,000,000
Additional share repurchase authorization							$ 5,000,000,000.0
Number of shares purchased (in shares)	1,400,000	3,000,000	2,700,000	2,500,000	9,600,000
Cost of shares repurchased	$ 170,000,000	$ 400,000,000	$ 350,000,000	$ 350,000,000	$ 1,270,000,000
Average price paid per share (in dollars per share)	$ 125.09	$ 130.22	$ 129.66	$ 141.84	$ 132.33
Remaining capacity under share repurchase authorization	$ 3,286,000,000	$ 3,456,000,000	$ 3,856,000,000	$ 4,206,000,000	$ 3,286,000,000
Cost of shares acquired to cover tax withholding costs and exercise costs					$ 51,000,000	$ 62,000,000