Common Stock - Shares Issued (Details) - shares	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
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)	3,049,400,000	3,084,000,000.0	3,275,800,000
Increase (Decrease) in Treasury Stock Shares
Treasury - balance at January 1 (in shares)	(1,020,912,567)
Total treasury - balance at December 31 (in shares)	(1,055,499,435)	(1,020,912,567)
Treasury stock
Increase (Decrease) in Treasury Stock Shares
Treasury - balance at January 1 (in shares)	(1,020,900,000)	(829,100,000)	(679,600,000)
Repurchase (in shares)	(50,000,000.0)	(213,000,000.0)	(181,500,000)
Reissuance: Employee benefit and compensation plans (in shares)	15,400,000	21,200,000	32,000,000.0
Reissuance: Warrant exercise (in shares)	0	0	9,400,000
Reissuance: Employee stock purchase plans (in shares)	1,200,000	800,000	900,000
Total treasury - balance at December 31 (in shares)	(1,055,500,000)	(1,020,900,000)	(829,100,000)
Treasury stock | Employee benefits and compensation plans
Increase (Decrease) in Treasury Stock Shares
Reissuance: Employee benefit and compensation plans (in shares)	14,200,000	20,400,000	21,700,000