Segment Information - Reportable Segments and Total Assets (Details) $ in Millions	3 Months Ended		6 Months Ended
	Mar. 31, 2021 USD ($) item	Sep. 30, 2020 item	Jun. 30, 2020 item	Dec. 31, 2020 USD ($)
Segment Reporting [Abstract]
Number of reporting segments | item	4	4	5
Summary of assets by segment
Total assets	$ 165,737			$ 165,883
Reportable segments | Advice and Wealth Management Segment
Summary of assets by segment
Total assets	21,833			21,266
Reportable segments | Asset Management Segment
Summary of assets by segment
Total assets	9,033			8,406
Reportable segments | Retirement & Protection Solutions Segment
Summary of assets by segment
Total assets	113,658			114,850
Reportable segments | Nonsegment
Summary of assets by segment
Total assets	$ 21,213			$ 21,361