Business Developments And Risks And Uncertainties (Narrative) (Detail) $ in Millions				1 Months Ended		12 Months Ended
	Feb. 10, 2021 USD ($)	Jan. 31, 2021 USD ($)	Jan. 01, 2020 USD ($)	Jan. 31, 2021 USD ($)	Dec. 31, 2020 USD ($)	Dec. 31, 2020 USD ($) segments	Jun. 17, 2019 USD ($)
Business Acquisition [Line Items]
Number of operating segments | segments						3
Federal legislation passed to combat the economic impact						$ 2,700,000
Additional corona virus relief aid package approved by congress					$ 900,000
Subsequent Event [Member]
Business Acquisition [Line Items]
New relief plan proposed to stabilize the financial system				$ 1,900,000
Subsequent Event [Member] | Credit Suisse [Member]
Business Acquisition [Line Items]
Damages Paid Value	$ 600
Damages Sought Value		$ 604		$ 604
GO And PBA Bonds [Member] | Subsequent Event [Member]
Business Acquisition [Line Items]
Outstanding bonds	$ 7,000
GO And PBA Bonds [Member] | Plan support agreement [Member]
Business Acquisition [Line Items]
Debt And Unsecured Claims Outstanding							$ 35,000
Puerto Rico [Member]
Business Acquisition [Line Items]
Claims payments			$ 51			391
Outstanding bonds					$ 2,900	$ 2,900