Total Equity and Other Comprehensive Income (Accumulated Other Comprehensive Income (Loss) Components) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2022	Mar. 31, 2021
Accumulated Other Comprehensive Income (Loss) [Line Items]
Equity, Beginning Balance	$ 55,726.0	$ 54,041.0
Other comprehensive income (loss), net of tax	(6,140.0)	(1,480.0)
Equity, Ending Balance	49,216.0	53,879.0
Transferred securities from available for sale to held to maturity	18,700.0
Net unrealized losses, related to securities transferred to held to maturity	1,300.0
Pretax loss included in AOCI from derivatives	(22.1)
Total
Accumulated Other Comprehensive Income (Loss) [Line Items]
Equity, Beginning Balance	409.0	2,770.0
Other comprehensive income (loss), net of tax	(6,140.0)	(1,480.0)
Equity, Ending Balance	(5,731.0)	1,290.0
Debt securities
Accumulated Other Comprehensive Income (Loss) [Line Items]
Equity, Beginning Balance	589.0	2,462.0
Other comprehensive income (loss), net of tax	(4,827.0)	(913.0)
Equity, Ending Balance	(4,238.0)	1,549.0
Cash flow hedge derivatives
Accumulated Other Comprehensive Income (Loss) [Line Items]
Equity, Beginning Balance	(201.0)	659.0
Other comprehensive income (loss), net of tax	(1,344.0)	(592.0)
Equity, Ending Balance	(1,545.0)	67.0
Pension and  other postretirement benefit plan adjustments
Accumulated Other Comprehensive Income (Loss) [Line Items]
Equity, Beginning Balance	27.0	(345.0)
Other comprehensive income (loss), net of tax	41.0	23.0
Equity, Ending Balance	68.0	(322.0)
Other
Accumulated Other Comprehensive Income (Loss) [Line Items]
Equity, Beginning Balance	(6.0)	(6.0)
Other comprehensive income (loss), net of tax	(10.0)	2.0
Equity, Ending Balance	$ (16.0)	$ (4.0)