Employee Benefit Plans (Schedule of Allocation of Plan Assets) (Details) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Defined Benefit Plan, Plan Assets, Allocation [Line Items]
Fair value of plan assets	$ 62,318	$ 36,225
Quoted price in active markets (Level 1) [Member]
Defined Benefit Plan, Plan Assets, Allocation [Line Items]
Fair value of plan assets	10,246	4,880
Significant other observable inputs (Level 2) [Member]
Defined Benefit Plan, Plan Assets, Allocation [Line Items]
Fair value of plan assets	23,065	15,489
Significant Unobservable Inputs (Level 3) [Member]
Defined Benefit Plan, Plan Assets, Allocation [Line Items]
Fair value of plan assets	1,649	1,671	$ 1,538
Fair Value Measured at Net Asset Value Per Share
Defined Benefit Plan, Plan Assets, Allocation [Line Items]
Fair value of plan assets	26,569	14,553
Global Equities [Member]
Defined Benefit Plan, Plan Assets, Allocation [Line Items]
Fair value of plan assets	8,442	3,593
Global Equities [Member] | Quoted price in active markets (Level 1) [Member]
Defined Benefit Plan, Plan Assets, Allocation [Line Items]
Fair value of plan assets	8,437	3,588
Global Equities [Member] | Significant other observable inputs (Level 2) [Member]
Defined Benefit Plan, Plan Assets, Allocation [Line Items]
Fair value of plan assets	5	5
Global Equities [Member] | Significant Unobservable Inputs (Level 3) [Member]
Defined Benefit Plan, Plan Assets, Allocation [Line Items]
Fair value of plan assets	0	0
Global Equities [Member] | Fair Value Measured at Net Asset Value Per Share
Defined Benefit Plan, Plan Assets, Allocation [Line Items]
Fair value of plan assets	0	0
Global Equity Commingled Funds [Member]
Defined Benefit Plan, Plan Assets, Allocation [Line Items]
Fair value of plan assets	2,687	1,496
Global Equity Commingled Funds [Member] | Quoted price in active markets (Level 1) [Member]
Defined Benefit Plan, Plan Assets, Allocation [Line Items]
Fair value of plan assets	1	0
Global Equity Commingled Funds [Member] | Significant other observable inputs (Level 2) [Member]
Defined Benefit Plan, Plan Assets, Allocation [Line Items]
Fair value of plan assets	2,686	1,496
Global Equity Commingled Funds [Member] | Significant Unobservable Inputs (Level 3) [Member]
Defined Benefit Plan, Plan Assets, Allocation [Line Items]
Fair value of plan assets	0	0
Global Equity Commingled Funds [Member] | Fair Value Measured at Net Asset Value Per Share
Defined Benefit Plan, Plan Assets, Allocation [Line Items]
Fair value of plan assets	0	0
Enhanced Global Equities [Member]
Defined Benefit Plan, Plan Assets, Allocation [Line Items]
Fair value of plan assets	241	715
Enhanced Global Equities [Member] | Quoted price in active markets (Level 1) [Member]
Defined Benefit Plan, Plan Assets, Allocation [Line Items]
Fair value of plan assets	56	322
Enhanced Global Equities [Member] | Significant other observable inputs (Level 2) [Member]
Defined Benefit Plan, Plan Assets, Allocation [Line Items]
Fair value of plan assets	185	393
Enhanced Global Equities [Member] | Significant Unobservable Inputs (Level 3) [Member]
Defined Benefit Plan, Plan Assets, Allocation [Line Items]
Fair value of plan assets	0	0
Enhanced Global Equities [Member] | Fair Value Measured at Net Asset Value Per Share
Defined Benefit Plan, Plan Assets, Allocation [Line Items]
Fair value of plan assets	0	0
Other Public Equities
Defined Benefit Plan, Plan Assets, Allocation [Line Items]
Fair value of plan assets	9,008	5,332
Other Public Equities | Quoted price in active markets (Level 1) [Member]
Defined Benefit Plan, Plan Assets, Allocation [Line Items]
Fair value of plan assets	0	0
Other Public Equities | Significant other observable inputs (Level 2) [Member]
Defined Benefit Plan, Plan Assets, Allocation [Line Items]
Fair value of plan assets	0	0
Other Public Equities | Significant Unobservable Inputs (Level 3) [Member]
Defined Benefit Plan, Plan Assets, Allocation [Line Items]
Fair value of plan assets	0	0
Other Public Equities | Fair Value Measured at Net Asset Value Per Share
Defined Benefit Plan, Plan Assets, Allocation [Line Items]
Fair value of plan assets	9,008	5,332
Private Equity Funds [Member]
Defined Benefit Plan, Plan Assets, Allocation [Line Items]
Fair value of plan assets	3,646	1,432
Private Equity Funds [Member] | Quoted price in active markets (Level 1) [Member]
Defined Benefit Plan, Plan Assets, Allocation [Line Items]
Fair value of plan assets	0	0
Private Equity Funds [Member] | Significant other observable inputs (Level 2) [Member]
Defined Benefit Plan, Plan Assets, Allocation [Line Items]
Fair value of plan assets	0	0
Private Equity Funds [Member] | Significant Unobservable Inputs (Level 3) [Member]
Defined Benefit Plan, Plan Assets, Allocation [Line Items]
Fair value of plan assets	0	202	133
Private Equity Funds [Member] | Fair Value Measured at Net Asset Value Per Share
Defined Benefit Plan, Plan Assets, Allocation [Line Items]
Fair value of plan assets	3,646	1,230
Governments [Member]
Defined Benefit Plan, Plan Assets, Allocation [Line Items]
Fair value of plan assets	3,220	1,085
Governments [Member] | Quoted price in active markets (Level 1) [Member]
Defined Benefit Plan, Plan Assets, Allocation [Line Items]
Fair value of plan assets	1,740	969
Governments [Member] | Significant other observable inputs (Level 2) [Member]
Defined Benefit Plan, Plan Assets, Allocation [Line Items]
Fair value of plan assets	1,480	116
Governments [Member] | Significant Unobservable Inputs (Level 3) [Member]
Defined Benefit Plan, Plan Assets, Allocation [Line Items]
Fair value of plan assets	0	0
Governments [Member] | Fair Value Measured at Net Asset Value Per Share
Defined Benefit Plan, Plan Assets, Allocation [Line Items]
Fair value of plan assets	0	0
Corporate Debt Securities [Member]
Defined Benefit Plan, Plan Assets, Allocation [Line Items]
Fair value of plan assets	18,799	13,065
Corporate Debt Securities [Member] | Quoted price in active markets (Level 1) [Member]
Defined Benefit Plan, Plan Assets, Allocation [Line Items]
Fair value of plan assets	3	1
Corporate Debt Securities [Member] | Significant other observable inputs (Level 2) [Member]
Defined Benefit Plan, Plan Assets, Allocation [Line Items]
Fair value of plan assets	18,489	13,059
Corporate Debt Securities [Member] | Significant Unobservable Inputs (Level 3) [Member]
Defined Benefit Plan, Plan Assets, Allocation [Line Items]
Fair value of plan assets	2	5	18
Corporate Debt Securities [Member] | Fair Value Measured at Net Asset Value Per Share
Defined Benefit Plan, Plan Assets, Allocation [Line Items]
Fair value of plan assets	305	0
Structured Products
Defined Benefit Plan, Plan Assets, Allocation [Line Items]
Fair value of plan assets	24	17
Structured Products | Quoted price in active markets (Level 1) [Member]
Defined Benefit Plan, Plan Assets, Allocation [Line Items]
Fair value of plan assets	0	0
Structured Products | Significant other observable inputs (Level 2) [Member]
Defined Benefit Plan, Plan Assets, Allocation [Line Items]
Fair value of plan assets	24	17
Structured Products | Significant Unobservable Inputs (Level 3) [Member]
Defined Benefit Plan, Plan Assets, Allocation [Line Items]
Fair value of plan assets	0	0
Structured Products | Fair Value Measured at Net Asset Value Per Share
Defined Benefit Plan, Plan Assets, Allocation [Line Items]
Fair value of plan assets	0	0
Fixed Income Securities [Member]
Defined Benefit Plan, Plan Assets, Allocation [Line Items]
Fair value of plan assets	6,631	4,755
Fixed Income Securities [Member] | Quoted price in active markets (Level 1) [Member]
Defined Benefit Plan, Plan Assets, Allocation [Line Items]
Fair value of plan assets	0	0
Fixed Income Securities [Member] | Significant other observable inputs (Level 2) [Member]
Defined Benefit Plan, Plan Assets, Allocation [Line Items]
Fair value of plan assets	0	0
Fixed Income Securities [Member] | Significant Unobservable Inputs (Level 3) [Member]
Defined Benefit Plan, Plan Assets, Allocation [Line Items]
Fair value of plan assets	0	0
Fixed Income Securities [Member] | Fair Value Measured at Net Asset Value Per Share
Defined Benefit Plan, Plan Assets, Allocation [Line Items]
Fair value of plan assets	6,631	4,755
Real Estate [Member]
Defined Benefit Plan, Plan Assets, Allocation [Line Items]
Fair value of plan assets	3,384	1,843
Real Estate [Member] | Quoted price in active markets (Level 1) [Member]
Defined Benefit Plan, Plan Assets, Allocation [Line Items]
Fair value of plan assets	0	0
Real Estate [Member] | Significant other observable inputs (Level 2) [Member]
Defined Benefit Plan, Plan Assets, Allocation [Line Items]
Fair value of plan assets	0	13
Real Estate [Member] | Significant Unobservable Inputs (Level 3) [Member]
Defined Benefit Plan, Plan Assets, Allocation [Line Items]
Fair value of plan assets	1,647	1,464	$ 1,387
Real Estate [Member] | Fair Value Measured at Net Asset Value Per Share
Defined Benefit Plan, Plan Assets, Allocation [Line Items]
Fair value of plan assets	1,737	366
Other Pension Plan Assets [Member]
Defined Benefit Plan, Plan Assets, Allocation [Line Items]
Fair value of plan assets	5,187	3,177
Other Pension Plan Assets [Member] | Quoted price in active markets (Level 1) [Member]
Defined Benefit Plan, Plan Assets, Allocation [Line Items]
Fair value of plan assets	0	0
Other Pension Plan Assets [Member] | Significant other observable inputs (Level 2) [Member]
Defined Benefit Plan, Plan Assets, Allocation [Line Items]
Fair value of plan assets	99	343
Other Pension Plan Assets [Member] | Significant Unobservable Inputs (Level 3) [Member]
Defined Benefit Plan, Plan Assets, Allocation [Line Items]
Fair value of plan assets	0	0
Other Pension Plan Assets [Member] | Fair Value Measured at Net Asset Value Per Share
Defined Benefit Plan, Plan Assets, Allocation [Line Items]
Fair value of plan assets	5,088	2,834
Cash & Cash Equivalents [Member]
Defined Benefit Plan, Plan Assets, Allocation [Line Items]
Fair value of plan assets	260	83
Cash & Cash Equivalents [Member] | Quoted price in active markets (Level 1) [Member]
Defined Benefit Plan, Plan Assets, Allocation [Line Items]
Fair value of plan assets	9	0
Cash & Cash Equivalents [Member] | Significant other observable inputs (Level 2) [Member]
Defined Benefit Plan, Plan Assets, Allocation [Line Items]
Fair value of plan assets	97	47
Cash & Cash Equivalents [Member] | Significant Unobservable Inputs (Level 3) [Member]
Defined Benefit Plan, Plan Assets, Allocation [Line Items]
Fair value of plan assets	0	0
Cash & Cash Equivalents [Member] | Fair Value Measured at Net Asset Value Per Share
Defined Benefit Plan, Plan Assets, Allocation [Line Items]
Fair value of plan assets	154	36
Pension Plan Assets Leveled [Member]
Defined Benefit Plan, Plan Assets, Allocation [Line Items]
Fair value of plan assets	61,529	36,593
Other Assets And Liabilities [Member]
Defined Benefit Plan, Plan Assets, Allocation [Line Items]
Fair value of plan assets	$ 789	$ (368)