Federal Funds Sold and Securities Borrowed or Purchased Under Agreements to Resell Securities Sold Under Agreements to Repurchase (Details) - USD ($) $ in Millions	Dec. 31, 2015	Dec. 31, 2014
securities sold under agreement to repurchase maturity [Line Items]
Securities Sold under Agreements to Repurchase	$ 1,654	$ 2,276
US Treasury Securities [Member]
securities sold under agreement to repurchase maturity [Line Items]
Securities Sold under Agreements to Repurchase	112	376
US Government Agencies Debt Securities [Member]
securities sold under agreement to repurchase maturity [Line Items]
Securities Sold under Agreements to Repurchase	319	231
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	860	1,104
Commercial Paper [Member]
securities sold under agreement to repurchase maturity [Line Items]
Securities Sold under Agreements to Repurchase	49	238
Corporate Debt Securities [Member]
securities sold under agreement to repurchase maturity [Line Items]
Securities Sold under Agreements to Repurchase	314	327
Maturity Overnight [Member]
securities sold under agreement to repurchase maturity [Line Items]
Securities Sold under Agreements to Repurchase	1,559	2,231
Maturity Overnight [Member] | US Treasury Securities [Member]
securities sold under agreement to repurchase maturity [Line Items]
Securities Sold under Agreements to Repurchase	112	376
Maturity Overnight [Member] | US Government Agencies Debt Securities [Member]
securities sold under agreement to repurchase maturity [Line Items]
Securities Sold under Agreements to Repurchase	319	231
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	837	1,059
Maturity Overnight [Member] | Commercial Paper [Member]
securities sold under agreement to repurchase maturity [Line Items]
Securities Sold under Agreements to Repurchase	49	238
Maturity Overnight [Member] | Corporate Debt Securities [Member]
securities sold under agreement to repurchase maturity [Line Items]
Securities Sold under Agreements to Repurchase	242	327
Maturity up to 30 days [Member]
securities sold under agreement to repurchase maturity [Line Items]
Securities Sold under Agreements to Repurchase	95	45
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	23	45
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	$ 72	$ 0