Retirement Benefits (Amounts Recorded in the Consolidated Statements of Income) (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Compensation and benefits expense (Operating income)	$ (621)	$ (541)	$ (691)	$ (908)	$ (670)	$ (535)	$ (701)	$ (749)	$ (2,761)	$ (2,655)	$ (2,431)
Other net benefit (credits) cost									(215)	(201)	(233)
Pension Plan
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Compensation and benefits expense (Operating income)									34	76	178
Other net benefit (credits) cost									(215)	(206)	(240)
Total (credit) cost									(181)	(130)	(62)
Postretirement Benefits
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Compensation and benefits expense (Operating income)									1	1	2
Other net benefit (credits) cost									0	5	7
Total (credit) cost									$ 1	$ 6	$ 9