Common Stock - Shares Issued (Details) - shares	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Increase (Decrease) in Common Stock Shares
Total issued - balance at January 1 (in shares)	4,104,933,895	4,104,900,000	4,104,900,000
Outstanding (in shares)	3,275,800,000	3,425,300,000	3,561,200,000
Increase (Decrease) in Treasury Stock Shares
Treasury - balance at January 1 (in shares)	(679,635,064)
Total treasury - balance at December 31 (in shares)	(829,167,674)	(679,635,064)
Treasury stock
Increase (Decrease) in Treasury Stock Shares
Treasury - balance at January 1 (in shares)	(679,600,000)	(543,700,000)	(441,400,000)
Repurchase (in shares)	(181,500,000)	(166,600,000)	(140,400,000)
Reissuance: Employee benefit and compensation plans (in shares)	32,000,000.0	30,700,000	38,100,000
Reissuance: Warrant exercise (in shares)	9,400,000	5,400,000	11,100,000
Reissuance: Employee stock purchase plans (in shares)	900,000	800,000	1,000,000.0
Total treasury - balance at December 31 (in shares)	(829,100,000)	(679,600,000)	(543,700,000)
Treasury stock | Employee benefits and compensation plans
Increase (Decrease) in Treasury Stock Shares
Reissuance: Employee benefit and compensation plans (in shares)	21,700,000	24,500,000	26,000,000.0