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, 2020	Dec. 31, 2019	Dec. 31, 2018
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	$ 19,074
Quoted Prices in Active Markets for Identical Assets (Level 1)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	4,600
Significant Other Observable Inputs (Level 2)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	7,562
Significant Unobservable Inputs (Level 3)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	774	$ 683	$ 334
NAV
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	6,138
Total investments
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	20,596	17,085
Total investments | Quoted Prices in Active Markets for Identical Assets (Level 1)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	4,600	3,930
Total investments | Significant Other Observable Inputs (Level 2)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	9,084	4,796
Total investments | Significant Unobservable Inputs (Level 3)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	774	683
Total investments | NAV
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	6,138	7,676
Common/collective trusts
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	4,859	6,451
Common/collective trusts | Quoted Prices in Active Markets for Identical Assets (Level 1)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	561	492
Common/collective trusts | Significant Other Observable Inputs (Level 2)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Common/collective trusts | Significant Unobservable Inputs (Level 3)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Common/collective trusts | NAV
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	4,298	5,959
Corporate obligations
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	4,709	4,063
Corporate obligations | Quoted Prices in Active Markets for Identical Assets (Level 1)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Corporate obligations | Significant Other Observable Inputs (Level 2)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	4,707	4,063
Corporate obligations | Significant Unobservable Inputs (Level 3)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	2	0
Corporate stocks
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	2,777	2,906
Corporate stocks | Quoted Prices in Active Markets for Identical Assets (Level 1)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	2,737	2,871
Corporate stocks | Significant Other Observable Inputs (Level 2)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	39	34
Corporate stocks | Significant Unobservable Inputs (Level 3)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	1	1	1
Private equity/partnerships
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	1,353	1,055
Private equity/partnerships | NAV
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	1,353	1,055
Government securities
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	4,346	699
Government securities | Quoted Prices in Active Markets for Identical Assets (Level 1)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	15	20
Government securities | Significant Other Observable Inputs (Level 2)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	4,331	679
Government securities | Significant 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	487	660
Real estate | NAV
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	487	660
Short-term investment funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	1,040	312
Short-term investment funds | Quoted Prices in Active Markets for Identical Assets (Level 1)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	1,040	309
Short-term investment funds | Significant Other Observable Inputs (Level 2)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	3
Short-term investment funds | Significant 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	234	223
Company common stock | Quoted Prices in Active Markets for Identical Assets (Level 1)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	234	223
Company common stock | Significant Other Observable Inputs (Level 2)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Company common stock | Significant 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	791	716
Other investments | Quoted Prices in Active Markets for Identical Assets (Level 1)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	13	15
Other investments | Significant Other Observable Inputs (Level 2)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	7	17
Other investments | Significant Unobservable Inputs (Level 3)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	771	682	$ 333
Other investments | NAV
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	$ 2
Net derivative liabilities
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	(1,522)
Net derivative liabilities | Quoted Prices in Active Markets for Identical Assets (Level 1)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0
Net derivative liabilities | Significant Other Observable Inputs (Level 2)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	(1,522)
Net derivative liabilities | Significant Unobservable Inputs (Level 3)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	$ 0