Offsetting Arrangements - Repo, Sec Lending Transactions Maturity By Category (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Assets Sold under Agreements to Repurchase [Line Items]
Repurchase agreements	$ 43,072	$ 35,509
Securities lending transactions	11,055	9,424
Gross amount of recognized liabilities for repurchase agreements and securities lending	54,127	44,933
Overnight and Continuous
Assets Sold under Agreements to Repurchase [Line Items]
Repurchase agreements	43,072	35,509
Securities lending transactions	11,055	8,390
Gross amount of recognized liabilities for repurchase agreements and securities lending	54,127	43,899
Up to 30 days
Assets Sold under Agreements to Repurchase [Line Items]
Repurchase agreements	0	0
Securities lending transactions	0	0
Gross amount of recognized liabilities for repurchase agreements and securities lending	0	0
30 – 90 days
Assets Sold under Agreements to Repurchase [Line Items]
Repurchase agreements	0	0
Securities lending transactions	0	1,034
Gross amount of recognized liabilities for repurchase agreements and securities lending	0	1,034
U.S. Treasury and agency securities
Assets Sold under Agreements to Repurchase [Line Items]
Repurchase agreements	43,072	35,509
U.S. Treasury and agency securities | Overnight and Continuous
Assets Sold under Agreements to Repurchase [Line Items]
Repurchase agreements	43,072	35,509
U.S. Treasury and agency securities | Up to 30 days
Assets Sold under Agreements to Repurchase [Line Items]
Repurchase agreements	0	0
U.S. Treasury and agency securities | 30 – 90 days
Assets Sold under Agreements to Repurchase [Line Items]
Repurchase agreements	0	0
Corporate debt securities
Assets Sold under Agreements to Repurchase [Line Items]
Securities lending transactions	35	53
Corporate debt securities | Overnight and Continuous
Assets Sold under Agreements to Repurchase [Line Items]
Securities lending transactions	35	53
Corporate debt securities | Up to 30 days
Assets Sold under Agreements to Repurchase [Line Items]
Securities lending transactions	0	0
Corporate debt securities | 30 – 90 days
Assets Sold under Agreements to Repurchase [Line Items]
Securities lending transactions	0	0
Equity securities
Assets Sold under Agreements to Repurchase [Line Items]
Securities lending transactions	11,020	9,371
Equity securities | Overnight and Continuous
Assets Sold under Agreements to Repurchase [Line Items]
Securities lending transactions	11,020	8,337
Equity securities | Up to 30 days
Assets Sold under Agreements to Repurchase [Line Items]
Securities lending transactions	0	0
Equity securities | 30 – 90 days
Assets Sold under Agreements to Repurchase [Line Items]
Securities lending transactions	0	$ 1,034
Non-U.S. sovereign debt
Assets Sold under Agreements to Repurchase [Line Items]
Securities lending transactions	0
Non-U.S. sovereign debt | Overnight and Continuous
Assets Sold under Agreements to Repurchase [Line Items]
Securities lending transactions	0
Non-U.S. sovereign debt | Up to 30 days
Assets Sold under Agreements to Repurchase [Line Items]
Securities lending transactions	0
Non-U.S. sovereign debt | 30 – 90 days
Assets Sold under Agreements to Repurchase [Line Items]
Securities lending transactions	$ 0