Investment Securities Investment Securities (Summary of Net Securities Gains (Losses)) (Details) - Debt securities - USD ($) $ in Millions	3 Months Ended
Mar. 31, 2020	Mar. 31, 2019
Investments, Debt, and Equity Securities [Abstract]
Securities gains	$ 0	$ 0
Securities losses	(1)	(8)
Net securities losses	$ (1)	$ (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.

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