Trading Securities (Net Gains (Losses) on Trading Securities) (Details) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Debt Securities, Trading, and Equity Securities, FV-NI [Abstract]
Trading Securities, Change in Unrealized Holding Gain (Loss)	$ 28	$ 15	$ 1

Amount of unrealized holding gain (loss) recognized in the income statement for investments in debt and equity securities and other forms of securities that provide ownership interests classified as trading.

No definition available.

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