Federal Funds Sold and Securities Borrowed or Purchased Under Agreements to Resell Securities Sold Under Agreements to Repurchase (Details) - USD ($) $ in Millions	Mar. 31, 2016	Dec. 31, 2015
securities sold under agreement to repurchase maturity [Line Items]
Securities Sold under Agreements to Repurchase	$ 1,774	$ 1,654
US Treasury Securities [Member]
securities sold under agreement to repurchase maturity [Line Items]
Securities Sold under Agreements to Repurchase	202	112
US Government Agencies Debt Securities [Member]
securities sold under agreement to repurchase maturity [Line Items]
Securities Sold under Agreements to Repurchase	126	319
Mortgage-backed Securities, Issued by US Government Sponsored Enterprises [Member]
securities sold under agreement to repurchase maturity [Line Items]
Securities Sold under Agreements to Repurchase	968	860
Commercial Paper [Member]
securities sold under agreement to repurchase maturity [Line Items]
Securities Sold under Agreements to Repurchase	205	49
Corporate Debt Securities [Member]
securities sold under agreement to repurchase maturity [Line Items]
Securities Sold under Agreements to Repurchase	273	314
Maturity Overnight [Member]
securities sold under agreement to repurchase maturity [Line Items]
Securities Sold under Agreements to Repurchase	1,679	1,559
Maturity Overnight [Member] | US Treasury Securities [Member]
securities sold under agreement to repurchase maturity [Line Items]
Securities Sold under Agreements to Repurchase	202	112
Maturity Overnight [Member] | US Government Agencies Debt Securities [Member]
securities sold under agreement to repurchase maturity [Line Items]
Securities Sold under Agreements to Repurchase	126	319
Maturity Overnight [Member] | Mortgage-backed Securities, Issued by US Government Sponsored Enterprises [Member]
securities sold under agreement to repurchase maturity [Line Items]
Securities Sold under Agreements to Repurchase	968	837
Maturity Overnight [Member] | Commercial Paper [Member]
securities sold under agreement to repurchase maturity [Line Items]
Securities Sold under Agreements to Repurchase	205	49
Maturity Overnight [Member] | Corporate Debt Securities [Member]
securities sold under agreement to repurchase maturity [Line Items]
Securities Sold under Agreements to Repurchase	178	242
Maturity up to 30 days [Member]
securities sold under agreement to repurchase maturity [Line Items]
Securities Sold under Agreements to Repurchase	95	95
Maturity up to 30 days [Member] | US Treasury Securities [Member]
securities sold under agreement to repurchase maturity [Line Items]
Securities Sold under Agreements to Repurchase	0	0
Maturity up to 30 days [Member] | US Government Agencies Debt Securities [Member]
securities sold under agreement to repurchase maturity [Line Items]
Securities Sold under Agreements to Repurchase	0	0
Maturity up to 30 days [Member] | Mortgage-backed Securities, Issued by US Government Sponsored Enterprises [Member]
securities sold under agreement to repurchase maturity [Line Items]
Securities Sold under Agreements to Repurchase	0	23
Maturity up to 30 days [Member] | Commercial Paper [Member]
securities sold under agreement to repurchase maturity [Line Items]
Securities Sold under Agreements to Repurchase	0	0
Maturity up to 30 days [Member] | Corporate Debt Securities [Member]
securities sold under agreement to repurchase maturity [Line Items]
Securities Sold under Agreements to Repurchase	$ 95	$ 72