Retirement Benefits (Components of the Net Periodic Benefit Cost) (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 Plan Disclosure [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 Plan Disclosure [Line Items]
Service cost									34	76	178
Interest cost									463	497	537
Expected return on plan assets									(864)	(921)	(940)
Amortization of prior service (credit) cost									(2)	(2)	(1)
Recognized actuarial loss (gain)									146	167	168
Compensation and benefits expense (Operating income)									34	76	178
Net periodic benefit (credit) cost									(223)	(183)	(58)
Curtailment (gain) loss									0	(1)	(4)
Settlement loss									42	54	0
Other net benefit (credits) cost									(215)	(206)	(240)
Total (credit) cost									(181)	(130)	(62)
Postretirement Benefits
Defined Benefit Plan Disclosure [Line Items]
Service cost									1	1	2
Interest cost									3	4	5
Expected return on plan assets									0	0	0
Amortization of prior service (credit) cost									(2)	1	4
Recognized actuarial loss (gain)									(1)		(2)
Compensation and benefits expense (Operating income)									1	1	2
Net periodic benefit (credit) cost									1	6	9
Curtailment (gain) loss									0	0	0
Settlement loss									0	0	0
Other net benefit (credits) cost									0	5	7
Total (credit) cost									1	6	9
United States | Pension Plan
Defined Benefit Plan Disclosure [Line Items]
Service cost									0	0	106
Interest cost									235	264	264
Expected return on plan assets									(357)	(357)	(379)
Amortization of prior service (credit) cost									0	0	0
Recognized actuarial loss (gain)									55	37	74
Net periodic benefit (credit) cost									(67)	(56)	65
United States | Postretirement Benefits
Defined Benefit Plan Disclosure [Line Items]
Service cost									0	0	0
Interest cost									1	2	2
Expected return on plan assets									0	0	0
Amortization of prior service (credit) cost									0	3	4
Recognized actuarial loss (gain)									(1)	(1)	(2)
Net periodic benefit (credit) cost									0	4	4
Foreign Plan | Pension Plan
Defined Benefit Plan Disclosure [Line Items]
Service cost									34	76	72
Interest cost									228	233	273
Expected return on plan assets									(507)	(564)	(561)
Amortization of prior service (credit) cost									(2)	(2)	(1)
Recognized actuarial loss (gain)									91	130	94
Net periodic benefit (credit) cost									(156)	(127)	(123)
Curtailment (gain) loss									0	(1)	(4)
Settlement loss									42	54	0
Total (credit) cost									(114)	(74)	(127)
Foreign Plan | Postretirement Benefits
Defined Benefit Plan Disclosure [Line Items]
Service cost									1	1	2
Interest cost									2	2	3
Expected return on plan assets									0	0	0
Amortization of prior service (credit) cost									(2)	(2)	0
Recognized actuarial loss (gain)									0	1	0
Net periodic benefit (credit) cost									1	2	5
Curtailment (gain) loss									0	0	0
Settlement loss									0	0	0
Total (credit) cost									$ 1	$ 2	$ 5