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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

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