Securities Financing Activities - Gross and Net Amounts of Securities Financing Agreements (Details) - USD ($)	Sep. 30, 2018	Dec. 31, 2017
Assets
Securities purchased under resale agreements, Gross amounts	$ 521,732,000,000	$ 448,608,000,000
Securities purchased under resale agreements, Amounts netted on the Consolidated balance sheets	(304,110,000,000)	(250,505,000,000)
Securities purchased under resale agreements, Amounts presented on the Consolidated balance sheets	217,622,000,000	198,103,000,000
Securities purchased under resale agreements, Amounts not nettable on the Consolidated balance sheets	(205,345,000,000)	(188,502,000,000)
Securities purchased under resale agreements, Net amounts	12,277,000,000	9,601,000,000
Securities borrowed, Gross amounts	143,644,000,000	113,926,000,000
Securities borrowed, Amounts netted on the Consolidated balance sheets	(21,210,000,000)	(8,814,000,000)
Securities borrowed, Amounts presented on the Consolidated balance sheets	122,434,000,000	105,112,000,000
Securities borrowed, Amounts not nettable on the Consolidated balance sheets	(89,771,000,000)	(76,805,000,000)
Securities borrowed, Net amounts	32,663,000,000	28,307,000,000
Liabilities
Securities sold under repurchase agreements, Gross amounts	472,560,000,000	398,218,000,000
Securities sold under repurchase agreements, Amounts netted on the Consolidated balance sheets	(304,110,000,000)	(250,505,000,000)
Securities sold under repurchase agreements, Amounts presented on the Consolidated balance sheets	168,450,000,000	147,713,000,000
Securities sold under repurchase agreements, Amounts not nettable on the Consolidated balance sheets	(154,335,000,000)	(129,178,000,000)
Securities sold under repurchase agreements, Net amounts	14,115,000,000	18,535,000,000
Securities loaned and other, Gross amounts	38,720,000,000	27,228,000,000
Securities loaned and other, Amounts netted on the Consolidated balance sheets	(21,210,000,000)	(8,814,000,000)
Securities loaned and other, Amounts presented on the Consolidated balance sheets	17,510,000,000	18,414,000,000
Securities loaned and other, Amounts not nettable on the Consolidated balance sheets	(17,146,000,000)	(18,151,000,000)
Securities loaned and other, Net amounts	364,000,000	263,000,000
Securities purchased under resale agreements where an appropriate legal opinion has not been either sought or obtained, Gross asset balance	6,400,000,000	7,500,000,000
Securities borrowed where an appropriate legal opinion has not been either sought or obtained	29,700,000,000	25,500,000,000
Securities sold under agreements to repurchase	13,200,000,000	16,500,000,000
Securities loaned and other	45,000,000	29,000,000
Securities-for-securities
Liabilities
Securities loaned and other, Amounts presented on the Consolidated balance sheets	5,200,000,000	9,200,000,000
Securities financing agreements accounted for at fair value
Assets
Securities purchased under resale agreements, Amounts presented on the Consolidated balance sheets	12,200,000,000	14,700,000,000
Liabilities
Securities sold under repurchase agreements, Amounts presented on the Consolidated balance sheets	1,100,000,000	697,000,000
Securities borrowed, fair value	4,500,000,000	3,000,000,000.0
Securities financing agreements accounted for at fair value | Securities loaned
Liabilities
Securities loaned accounted for at fair value	$ 0	$ 0