Investments in Securities Trading 2 (Details) - USD ($) $ in Millions	3 Months Ended	9 Months Ended
Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Debt and Equity Securities, FV-NI [Line Items]
Net trading gains	$ (40)	$ 59	$ 79	$ 145
Net trading gains (losses) recognized in the period related to securities still held at period end	$ (27)	$ 51	$ 20	$ 125

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