Accumulated Other Comprehensive Income (Loss), Net of Tax Accumulated Other Comprehensive Income (Loss), Net of Tax (Reclassifications out of AOCI) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Accumulated Other Comprehensive Income (Loss) [Line Items]
Amount Reclassified from Accumulated Other Comprehensive Income, Pre-Tax	$ (15)	$ 12	$ (8)
Amount Reclassified from Accumulated Other Comprehensive Income, Tax	4	(8)	1
Amount Reclassified from Accumulated Other Comprehensive Income, After-Tax	(11)	4	(7)
Accumulated Net Unrealized Investment Gain (Loss) [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Amount Reclassified from AOCI for Available for Sale Securities, Pre-Tax	9	42	13
Amount Reclassified from AOCI for Available for Sale Securities, Tax	(3)	(16)	(5)
Amount Reclassified from AOCI for Available for Sale Securities, After-Tax	6	26	8
Amount Reclassified from Accumulated Other Comprehensive Income, After-Tax	6	26	8
Accumulated Defined Benefit Plans Adjustment [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Amount Reclassified from AOCI for Pension and OPEB Plans, Pre-Tax	(20)	(16)	(17)
Amount Reclassified from AOCI for Pension and OPEB Plans, Tax	6	4	5
Amount Reclassified from AOCI for Pension and OPEB Plans, After-Tax	(14)	(12)	(12)
Amount Reclassified from Accumulated Other Comprehensive Income, After-Tax	(14)	(12)	(12)
Accumulated Net Gain (Loss) from Designated or Qualifying Cash Flow Hedges [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Amount Reclassified from AOCI for Cash Flow Hedges, Pre-Tax	(4)	(14)	(4)
Amount Reclassified from AOCI for Cash Flow Hedges, Tax	1	4	1
Amount Reclassified from AOCI for Cash Flow Hedges, After-Tax	(3)	(10)	(3)
Amount Reclassified from Accumulated Other Comprehensive Income, After-Tax	(3)	(10)	(3)
Net Gains (Losses) on Trust Investments [Member] | Accumulated Net Unrealized Investment Gain (Loss) [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Amount Reclassified from AOCI for Available for Sale Securities, Pre-Tax	9	42	13
Amount Reclassified from AOCI for Available for Sale Securities, Tax	(3)	(16)	(5)
Amount Reclassified from AOCI for Available for Sale Securities, After-Tax	6	26	8
Interest Expense [Member] | Accumulated Net Gain (Loss) from Designated or Qualifying Cash Flow Hedges [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Amount Reclassified from AOCI for Cash Flow Hedges, Pre-Tax	(4)	(14)	(4)
Amount Reclassified from AOCI for Cash Flow Hedges, Tax	1	4	1
Amount Reclassified from AOCI for Cash Flow Hedges, After-Tax	(3)	(10)	(3)
Non-Operating Pension and OPEB Credits (Costs) [Member] | Accumulated Defined Benefit Plans Adjustment [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Amortization of Prior Service (Cost) Credit, Pre-Tax	21	24	26
Amortization of Prior Service (Cost) Credit, Tax	(6)	(7)	(7)
Amortization of Prior Service (Cost) Credit, After-Tax	15	17	19
Amortization of Actuarial Loss, Pre-Tax	(41)	(40)	(43)
Amortization of Actuarial Loss, Tax	12	11	12
Amortization of Actuarial Loss, After-Tax	$ (29)	$ (29)	$ (31)