Retirement Benefits (Summary of the U.S. and Non-U.S. Plan Investments Measured At Fair Value on a Recurring Basis) (Details) - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017
Defined Benefit Plan Disclosure [Line Items]
Investments measured at NAV	$ 6,813	$ 8,980
Total investments	14,378	16,176
Identical Assets (Level 1)
Defined Benefit Plan Disclosure [Line Items]
Total investments	2,970	2,586
Observable Inputs (Level 2)
Defined Benefit Plan Disclosure [Line Items]
Total investments	4,261	4,238
Unobservable Inputs (Level 3)
Defined Benefit Plan Disclosure [Line Items]
Total investments	334	372
Common/Collective trusts
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	5,620	7,986
Investments measured at NAV	5,329	7,611
Common/Collective trusts | Identical Assets (Level 1)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	291	375
Common/Collective trusts | Observable Inputs (Level 2)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Common/Collective trusts | Unobservable Inputs (Level 3)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Corporate Obligations
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	3,673	3,640
Investments measured at NAV	0	0
Corporate Obligations | Identical Assets (Level 1)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Corporate Obligations | Observable Inputs (Level 2)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	3,673	3,620
Corporate Obligations | Unobservable Inputs (Level 3)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	20
Corporate stocks
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	2,080	1,503
Investments measured at NAV	0	0
Corporate stocks | Identical Assets (Level 1)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	2,046	1,467
Corporate stocks | Observable Inputs (Level 2)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	33	34
Corporate stocks | Unobservable Inputs (Level 3)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	1	2
Private equity/partnerships
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	921	803
Investments measured at NAV	921	803
Private equity/partnerships | Identical Assets (Level 1)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Private equity/partnerships | Observable Inputs (Level 2)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Private equity/partnerships | Unobservable Inputs (Level 3)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Government Securities
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	550	571
Investments measured at NAV	0	0
Government Securities | Identical Assets (Level 1)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	15	15
Government Securities | Observable Inputs (Level 2)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	535	556
Government Securities | Unobservable Inputs (Level 3)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Real Estate
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	563	566
Investments measured at NAV	563	566
Real Estate | Identical Assets (Level 1)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Real Estate | Observable Inputs (Level 2)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Real Estate | Unobservable Inputs (Level 3)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Short-term investment funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	286	407
Investments measured at NAV	0	0
Short-term investment funds | Identical Assets (Level 1)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	286	391
Short-term investment funds | Observable Inputs (Level 2)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	16
Short-term investment funds | Unobservable Inputs (Level 3)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Company common stock
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	319	326
Investments measured at NAV	0	0
Company common stock | Identical Assets (Level 1)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	319	326
Company common stock | Observable Inputs (Level 2)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Company common stock | Unobservable Inputs (Level 3)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Other Investments
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	366	374
Investments measured at NAV	0	0
Other Investments | Identical Assets (Level 1)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	13	12
Other Investments | Observable Inputs (Level 2)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	20	12
Other Investments | Unobservable Inputs (Level 3)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	$ 333	$ 350