Compensation and Benefit Plans (Pension Plan Assets - Fair Value Levels) (Details) - Pension Plans - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Pension and Other Postretirement Benefits
Fair value of plan assets	$ 3,714	$ 3,548
Fair value NAV	1,363	1,284
Receivables and payables, net	(98)	(160)
Net plan assets available for benefits	3,616	3,388	$ 3,298
Level 1
Pension and Other Postretirement Benefits
Fair value of plan assets	1,051	1,103
Level 2
Pension and Other Postretirement Benefits
Fair value of plan assets	1,300	1,161
Level 3
Pension and Other Postretirement Benefits
Fair value of plan assets	0	0
U.S. government and agency securities
Pension and Other Postretirement Benefits
Fair value of plan assets	691	526
Fair value NAV	0	0
U.S. government and agency securities | Level 1
Pension and Other Postretirement Benefits
Fair value of plan assets	184	217
U.S. government and agency securities | Level 2
Pension and Other Postretirement Benefits
Fair value of plan assets	507	309
U.S. government and agency securities | Level 3
Pension and Other Postretirement Benefits
Fair value of plan assets	0	0
Corporate stocks
Pension and Other Postretirement Benefits
Fair value of plan assets	729	735
Fair value NAV	$ 0	$ 0
Corporate stocks | Russell Indexes
Pension and Other Postretirement Benefits
Performance percentage benchmark, percentage	54.00%	62.00%
Corporate stocks | MSCI
Pension and Other Postretirement Benefits
Performance percentage benchmark, percentage	46.00%	38.00%
Corporate stocks | Level 1
Pension and Other Postretirement Benefits
Fair value of plan assets	$ 718	$ 720
Corporate stocks | Level 2
Pension and Other Postretirement Benefits
Fair value of plan assets	11	15
Corporate stocks | Level 3
Pension and Other Postretirement Benefits
Fair value of plan assets	0	0
Corporate bonds
Pension and Other Postretirement Benefits
Fair value of plan assets	676	725
Fair value NAV	0	0
Corporate bonds | Level 1
Pension and Other Postretirement Benefits
Fair value of plan assets	0	0
Corporate bonds | Level 2
Pension and Other Postretirement Benefits
Fair value of plan assets	676	725
Corporate bonds | Level 3
Pension and Other Postretirement Benefits
Fair value of plan assets	0	0
Common/collective funds
Pension and Other Postretirement Benefits
Fair value of plan assets	705	692
Fair value NAV	$ 705	$ 692
Common/collective funds | Standard and Poor's 500
Pension and Other Postretirement Benefits
Performance percentage benchmark, percentage	41.00%	45.00%
Common/collective funds | Russell 1000 index
Pension and Other Postretirement Benefits
Performance percentage benchmark, percentage	15.00%	15.00%
Common/collective funds | MSCI All Country World Index exUS
Pension and Other Postretirement Benefits
Performance percentage benchmark, percentage	15.00%	15.00%
Common/collective funds | Non-index U.S. equity fund
Pension and Other Postretirement Benefits
Performance percentage benchmark, percentage	25.00%	23.00%
Common/collective funds | Level 1
Pension and Other Postretirement Benefits
Fair value of plan assets	$ 0	$ 0
Common/collective funds | Level 2
Pension and Other Postretirement Benefits
Fair value of plan assets	0	0
Common/collective funds | Level 3
Pension and Other Postretirement Benefits
Fair value of plan assets	0	0
Partnerships/joint ventures
Pension and Other Postretirement Benefits
Fair value of plan assets	396	333
Fair value NAV	$ 396	$ 333
Partnerships/joint ventures | Private equity and venture capital funds including branded consumer products, clean and information technology and healthcare
Pension and Other Postretirement Benefits
Actual plan asset allocations, percentage	55.00%	55.00%
Partnerships/joint ventures | Publicly traded fixed income securities
Pension and Other Postretirement Benefits
Actual plan asset allocations, percentage	23.00%	22.00%
Partnerships/joint ventures | Broad range of financial assets in all global markets
Pension and Other Postretirement Benefits
Actual plan asset allocations, percentage	20.00%	18.00%
Partnerships/joint ventures | Asset backed securities including distressed mortgages
Pension and Other Postretirement Benefits
Actual plan asset allocations, percentage	2.00%	4.00%
Partnerships/joint ventures | Level 1
Pension and Other Postretirement Benefits
Fair value of plan assets	$ 0	$ 0
Partnerships/joint ventures | Level 2
Pension and Other Postretirement Benefits
Fair value of plan assets	0	0
Partnerships/joint ventures | Level 3
Pension and Other Postretirement Benefits
Fair value of plan assets	0	0
Other investment entities
Pension and Other Postretirement Benefits
Fair value of plan assets	262	253
Fair value NAV	262	253
Other investment entities | Level 1
Pension and Other Postretirement Benefits
Fair value of plan assets	0	0
Other investment entities | Level 2
Pension and Other Postretirement Benefits
Fair value of plan assets	0	0
Other investment entities | Level 3
Pension and Other Postretirement Benefits
Fair value of plan assets	0	0
Registered investment companies
Pension and Other Postretirement Benefits
Fair value of plan assets	140	130
Fair value NAV	0	6
Registered investment companies | Level 1
Pension and Other Postretirement Benefits
Fair value of plan assets	140	124
Registered investment companies | Level 2
Pension and Other Postretirement Benefits
Fair value of plan assets	0	0
Registered investment companies | Level 3
Pension and Other Postretirement Benefits
Fair value of plan assets	0	0
Interest-bearing cash
Pension and Other Postretirement Benefits
Fair value of plan assets	9	42
Fair value NAV	0	0
Interest-bearing cash | Level 1
Pension and Other Postretirement Benefits
Fair value of plan assets	9	42
Interest-bearing cash | Level 2
Pension and Other Postretirement Benefits
Fair value of plan assets	0	0
Interest-bearing cash | Level 3
Pension and Other Postretirement Benefits
Fair value of plan assets	0	0
Other
Pension and Other Postretirement Benefits
Fair value of plan assets	106	112
Fair value NAV	0	0
Other | Level 1
Pension and Other Postretirement Benefits
Fair value of plan assets	0	0
Other | Level 2
Pension and Other Postretirement Benefits
Fair value of plan assets	106	112
Other | Level 3
Pension and Other Postretirement Benefits
Fair value of plan assets	0	0
Collateralized mortgage obligations and other asset backed securities
Pension and Other Postretirement Benefits
Fair value of plan assets	65	76
Mortgage obligations and other asset backed securities, below investment grade	18	27
SCE
Pension and Other Postretirement Benefits
Net plan assets available for benefits	$ 3,390	$ 3,172	$ 3,080