Significant Accounting Policies (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Jan. 01, 2018
Buildings
Premises, Equipment and Software Costs
Estimated useful lives	39 years
Leasehold Improvements - Building \| Maximum
Premises, Equipment and Software Costs
Estimated useful lives	25 years
Leasehold Improvements - Other \| Maximum
Premises, Equipment and Software Costs
Estimated useful lives	15 years
Furniture and Fixtures
Premises, Equipment and Software Costs
Estimated useful lives	7 years
Computer and Communications Equipment \| Minimum
Premises, Equipment and Software Costs
Estimated useful lives	3 years
Computer and Communications Equipment \| Maximum
Premises, Equipment and Software Costs
Estimated useful lives	9 years
Power Generation Assets \| Minimum
Premises, Equipment and Software Costs
Estimated useful lives	15 years
Power Generation Assets \| Maximum
Premises, Equipment and Software Costs
Estimated useful lives	29 years
Terminals, Pipelines and Equipment \| Minimum
Premises, Equipment and Software Costs
Estimated useful lives	3 years
Terminals, Pipelines and Equipment \| Maximum
Premises, Equipment and Software Costs
Estimated useful lives	30 years
Software Costs \| Minimum
Premises, Equipment and Software Costs
Estimated useful lives	2 years
Software Costs \| Maximum
Premises, Equipment and Software Costs
Estimated useful lives	10 years
Revenue from Contracts with Customers
Accounting Standards Adopted
Cumulative catch-up adjustment to Retained Earnings		$ (32)
Derivatives and Hedging-Targeted Improvements to Accounting for Hedging Activities
Accounting Standards Adopted
Cumulative catch-up adjustment to Retained Earnings		(99)
Reclassification of Certain Tax Effects from Accumulated Other Comprehensive Income
Accounting Standards Adopted
Cumulative catch-up adjustment to Retained Earnings		$ 443