Employee Incentive, Retirement, Deferred Compensation, and Career Achievement Plans (Information on Stock Options Granted and Exercised) (Details) - USD ($) $ / shares in Units, $ in Millions		12 Months Ended
		Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Retirement Benefits [Abstract]
Weighted-average fair value of options granted per share (USD per share)		$ 11.56	$ 11.97	$ 14.16
Cash received from options exercised	[1]	$ 79	$ 118	$ 125
Tax benefit realized on options exercised		11	17	35
Aggregate intrinsic value of options exercised		$ 71	$ 108	$ 189

[1] Certain prior year amounts have been reclassified to conform to the current year presentation. See Note 1 for additional information.