Offsetting Arrangements - Repo, Sec Lending Transactions Maturity By Category (Details) - USD ($) $ in Millions	Sep. 30, 2018	Dec. 31, 2017
Assets Sold under Agreements to Repurchase [Line Items]
Repurchase agreements	$ 49,858
Securities lending transactions	19,599
Derivative Liability, Securities Sold under Agreements to Repurchase, Securities Loaned, Gross	69,457
U.S. Treasury and agency securities
Assets Sold under Agreements to Repurchase [Line Items]
Repurchase agreements	49,858
Securities lending transactions	209
Corporate debt securities
Assets Sold under Agreements to Repurchase [Line Items]
Securities lending transactions	80
Equity securities
Assets Sold under Agreements to Repurchase [Line Items]
Securities lending transactions	10,805
Other(2)
Assets Sold under Agreements to Repurchase [Line Items]
Securities lending transactions	8,505
Overnight and Continuous
Assets Sold under Agreements to Repurchase [Line Items]
Repurchase agreements	49,858	$ 43,072
Securities lending transactions	19,431	11,055
Derivative Liability, Securities Sold under Agreements to Repurchase, Securities Loaned, Gross	69,289	54,127
Overnight and Continuous | U.S. Treasury and agency securities
Assets Sold under Agreements to Repurchase [Line Items]
Repurchase agreements	49,858	43,072
Securities lending transactions	209	0
Overnight and Continuous | Corporate debt securities
Assets Sold under Agreements to Repurchase [Line Items]
Securities lending transactions	80	35
Overnight and Continuous | Equity securities
Assets Sold under Agreements to Repurchase [Line Items]
Securities lending transactions	10,637	11,020
Overnight and Continuous | Other(2)
Assets Sold under Agreements to Repurchase [Line Items]
Securities lending transactions	8,505	$ 0
Up to 30 Days
Assets Sold under Agreements to Repurchase [Line Items]
Repurchase agreements	0
Securities lending transactions	168
Derivative Liability, Securities Sold under Agreements to Repurchase, Securities Loaned, Gross	168
Up to 30 Days | U.S. Treasury and agency securities
Assets Sold under Agreements to Repurchase [Line Items]
Repurchase agreements	0
Securities lending transactions	0
Up to 30 Days | Corporate debt securities
Assets Sold under Agreements to Repurchase [Line Items]
Securities lending transactions	0
Up to 30 Days | Equity securities
Assets Sold under Agreements to Repurchase [Line Items]
Securities lending transactions	168
Up to 30 Days | Other(2)
Assets Sold under Agreements to Repurchase [Line Items]
Securities lending transactions	$ 0