Offsetting Arrangements - Repo, Sec Lending Transactions Maturity By Category (Details) - USD ($) $ in Millions	Jun. 30, 2018	Dec. 31, 2017
Assets Sold under Agreements to Repurchase [Line Items]
Repurchase agreements	$ 45,123
Securities lending transactions	15,964
Derivative Liability, Securities Sold under Agreements to Repurchase, Securities Loaned, Gross	61,087
U.S. Treasury and agency securities
Assets Sold under Agreements to Repurchase [Line Items]
Repurchase agreements	45,123
Securities lending transactions	115
Corporate debt securities
Assets Sold under Agreements to Repurchase [Line Items]
Securities lending transactions	88
Equity securities
Assets Sold under Agreements to Repurchase [Line Items]
Securities lending transactions	8,761
Other(2)
Assets Sold under Agreements to Repurchase [Line Items]
Securities lending transactions	7,000
Overnight and Continuous
Assets Sold under Agreements to Repurchase [Line Items]
Repurchase agreements	45,123	$ 43,072
Securities lending transactions	15,799	11,055
Derivative Liability, Securities Sold under Agreements to Repurchase, Securities Loaned, Gross	60,922	54,127
Overnight and Continuous | U.S. Treasury and agency securities
Assets Sold under Agreements to Repurchase [Line Items]
Repurchase agreements	45,123	43,072
Securities lending transactions	115	0
Overnight and Continuous | Corporate debt securities
Assets Sold under Agreements to Repurchase [Line Items]
Securities lending transactions	88	35
Overnight and Continuous | Equity securities
Assets Sold under Agreements to Repurchase [Line Items]
Securities lending transactions	8,596	11,020
Overnight and Continuous | Other(2)
Assets Sold under Agreements to Repurchase [Line Items]
Securities lending transactions	7,000	$ 0
Up to 30 Days
Assets Sold under Agreements to Repurchase [Line Items]
Repurchase agreements	0
Securities lending transactions	165
Derivative Liability, Securities Sold under Agreements to Repurchase, Securities Loaned, Gross	165
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	165
Up to 30 Days | Other(2)
Assets Sold under Agreements to Repurchase [Line Items]
Securities lending transactions	$ 0