Investment Securities Investment Securities (Summary of Net Securities Gains (Losses)) (Details) - Debt securities - USD ($) $ in Millions	3 Months Ended	9 Months Ended
Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Investments, Debt, and Equity Securities [Abstract]
Securities gains	$ 0	$ 0	$ 1	$ 0
Securities losses	0	0	(1)	(8)
Net securities losses	$ 0	$ 0	$ 0	$ (8)

This item represents the difference between the gross realized gains and losses realized on the sale of debt or equity securities categorized neither as held-to-maturity nor trading securities. Additionally, this item would include any losses recognized for other than temporary impairments (OTTI) of the subject investments in debt and equity securities.

No definition available.

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration