Business Acquisitions (TD Ameritrade Narrative) (Details) account in Millions, $ in Millions		3 Months Ended	9 Months Ended
	Oct. 06, 2020 USD ($) account shares	Sep. 30, 2020 USD ($)	Sep. 30, 2020 USD ($)	Sep. 30, 2019 USD ($)	Dec. 31, 2019 USD ($)
Business Acquisition [Line Items]
Goodwill		$ 1,737	$ 1,737		$ 1,227
TD Ameritrade [Member]
Business Acquisition [Line Items]
Acquisition costs		$ 42	$ 103	$ 1
TD Ameritrade [Member] | Subsequent Event [Member]
Business Acquisition [Line Items]
Total client assets	$ 6,000,000
Total number of portfolio accounts | account	29
Conversion of shares (in shares) | shares	1.0837
Number of shares issued in acquisition (in shares) | shares	586,000,000
Equipment, office facilities, and property	$ 466
Estimated Fair Value	8,880
Goodwill	10,264
Professional services expense	$ 26
TD Ameritrade [Member] | Common Stock [Member] | Subsequent Event [Member]
Business Acquisition [Line Items]
Number of shares issued in acquisition (in shares) | shares	509,000,000
TD Ameritrade [Member] | Common Stock [Member] | Subsequent Event [Member] | TD Bank [Member]
Business Acquisition [Line Items]
Number of shares issued in acquisition (in shares) | shares	177,000,000
TD Ameritrade [Member] | Common Stock - Nonvoting [Member] | Subsequent Event [Member] | TD Bank [Member]
Business Acquisition [Line Items]
Number of shares issued in acquisition (in shares) | shares	77,000,000