Compensation and Benefit Plans (Other Postretirement Plan Assets - Fair Value Levels) (Details) - PBOP - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value of plan assets	$ 2,713	$ 2,484
Receivables and payables, net	4	(19)
Net plan assets available for benefits	2,717	2,465	$ 2,133
Level 1
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value of plan assets	669	696
Level 2
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value of plan assets	1,270	1,068
NAV
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value of plan assets	774	720
U.S. government and agency securities
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value of plan assets	410	449
U.S. government and agency securities | Level 1
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value of plan assets	380	386
U.S. government and agency securities | Level 2
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value of plan assets	30	63
U.S. government and agency securities | NAV
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value of plan assets	0	0
Corporate stocks
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value of plan assets	$ 227	$ 244
Corporate stocks | Russell Indexes
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Performance percentage benchmark, percentage	70.00%	68.00%
Corporate stocks | MSCI All Country World Index
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Performance percentage benchmark, percentage	30.00%	32.00%
Corporate stocks | Level 1
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value of plan assets	$ 224	$ 242
Corporate stocks | Level 2
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value of plan assets	3	2
Corporate stocks | NAV
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value of plan assets	0	0
Corporate notes and bonds
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value of plan assets	1,079	885
Corporate notes and bonds | Level 1
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value of plan assets	0	0
Corporate notes and bonds | Level 2
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value of plan assets	1,079	885
Corporate notes and bonds | NAV
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value of plan assets	0	0
Common/collective funds
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value of plan assets	$ 693	$ 652
Common/collective funds | Non-index U.S. equity fund
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Actual plan asset allocations, percentage	22.00%	19.00%
Common/collective funds | Level 1
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value of plan assets	$ 0	$ 0
Common/collective funds | Level 2
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value of plan assets	0	0
Common/collective funds | NAV
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value of plan assets	693	652
Partnerships
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value of plan assets	$ 81	$ 68
Partnerships | Private equity
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Actual plan asset allocations, percentage	46.00%	55.00%
Partnerships | Broad range of financial assets in all global markets
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Actual plan asset allocations, percentage	18.00%	15.00%
Partnerships | Asset backed securities including distressed mortgages
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Actual plan asset allocations, percentage	36.00%	28.00%
Partnerships | Level 1
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value of plan assets	$ 0	$ 0
Partnerships | Level 2
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value of plan assets	0	0
Partnerships | NAV
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value of plan assets	81	68
Registered investment companies
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value of plan assets	65	66
Registered investment companies | Level 1
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value of plan assets	65	66
Registered investment companies | Level 2
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value of plan assets	0	0
Registered investment companies | NAV
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value of plan assets	0	0
Interest bearing cash
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value of plan assets	26	17
Interest bearing cash | Level 1
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value of plan assets	0	0
Interest bearing cash | Level 2
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value of plan assets	26	17
Interest bearing cash | NAV
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value of plan assets	0	0
Other
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value of plan assets	132	103
Other | Municipal securities
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value of plan assets	61	66
Other | Level 1
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value of plan assets	0	2
Other | Level 2
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value of plan assets	132	101
Other | NAV
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Fair value of plan assets	0	0
Collateralized mortgage obligations and other asset backed securities
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Receivables and payables, net	170	49
SCE
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Net plan assets available for benefits	$ 2,717	$ 2,464	$ 2,133