Employee Benefit Plans (Pension Plans) (Level 3 Significant Unobservable Inputs) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Defined Benefit Plan Disclosure [Line Items]
Beginning Balance, Plan Assets	$ 36,225
Ending Balance, Plan Assets	62,318	$ 36,225
Significant Unobservable Inputs (Level 3) [Member]
Defined Benefit Plan Disclosure [Line Items]
Beginning Balance, Plan Assets	1,671	1,538
Realized gains (losses)	7	(2)
Unrealized gains (losses) relating to instruments still held in the reporting period	(113)	59
Purchases, sales and settlements, net	84	76
Transfers in/out, net	0
Ending Balance, Plan Assets	1,649	1,671
Private Equities
Defined Benefit Plan Disclosure [Line Items]
Beginning Balance, Plan Assets	1,432
Ending Balance, Plan Assets	3,646	1,432
Private Equities | Significant Unobservable Inputs (Level 3) [Member]
Defined Benefit Plan Disclosure [Line Items]
Beginning Balance, Plan Assets	202	133
Realized gains (losses)	0	0
Unrealized gains (losses) relating to instruments still held in the reporting period	16	32
Purchases, sales and settlements, net	10	37
Transfers in/out, net	(228)
Ending Balance, Plan Assets	0	202
Corporate Bonds [Member]
Defined Benefit Plan Disclosure [Line Items]
Beginning Balance, Plan Assets	13,065
Ending Balance, Plan Assets	18,799	13,065
Corporate Bonds [Member] | Significant Unobservable Inputs (Level 3) [Member]
Defined Benefit Plan Disclosure [Line Items]
Beginning Balance, Plan Assets	5	18
Realized gains (losses)	0	0
Unrealized gains (losses) relating to instruments still held in the reporting period	0	0
Purchases, sales and settlements, net	(3)	(13)
Transfers in/out, net	0
Ending Balance, Plan Assets	2	5
Real Estate [Member]
Defined Benefit Plan Disclosure [Line Items]
Beginning Balance, Plan Assets	1,843
Ending Balance, Plan Assets	3,384	1,843
Real Estate [Member] | Significant Unobservable Inputs (Level 3) [Member]
Defined Benefit Plan Disclosure [Line Items]
Beginning Balance, Plan Assets	1,464	1,387
Realized gains (losses)	7	(2)
Unrealized gains (losses) relating to instruments still held in the reporting period	(129)	27
Purchases, sales and settlements, net	77	52
Transfers in/out, net	228
Ending Balance, Plan Assets	$ 1,647	$ 1,464