Retirement Benefits (Amounts Recorded in the Consolidated Statements of Income) (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Compensation and benefits expense (Operating income)	$ (592)	$ (467)	$ (680)	$ (938)	$ (621)	$ (541)	$ (691)	$ (908)	$ (2,677)	$ (2,761)	$ (2,655)
Other net benefit (credit) cost									(265)	(215)	(201)
Pension Benefits
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Compensation and benefits expense (Operating income)									31	34	76
Other net benefit (credit) cost									(265)	(215)	(206)
Total (credit) cost									(234)	(181)	(130)
Post-retirement Benefits
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Compensation and benefits expense (Operating income)									0	1	1
Other net benefit (credit) cost									0	0	5
Total (credit) cost									$ 0	$ 1	$ 6