Business Acquisitions (TD Ameritrade Narrative) (Details) shares in Millions, $ in Millions		3 Months Ended	9 Months Ended
	Oct. 06, 2020 USD ($) shares	Sep. 30, 2020 USD ($)	Sep. 30, 2020 USD ($)	Sep. 30, 2021 shares	Oct. 05, 2020
Business Acquisition [Line Items]
Basis spread on variable rate	0.15%				0.25%
TD Ameritrade Holding [Member]
Business Acquisition [Line Items]
Purchase price | $	$ 21,800
Conversion ratio for shares in acquisition	1.0837
Number of shares issued in acquisition (in shares)	586
Pro forma, acquisitions costs | $		$ 13	$ 51
TD Ameritrade Holding [Member] | Common Stock [Member]
Business Acquisition [Line Items]
Number of shares issued in acquisition (in shares)	509
TD Ameritrade Holding [Member] | Nonvoting Common Stock [Member] | TD Bank [Member]
Business Acquisition [Line Items]
Number of shares issued in acquisition (in shares)	77
Number of shares held (in shares)				79