Federal Funds Sold and Securities Financing Activities Securities Sold Under Agreements to Repurchase (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
securities sold under agreement to repurchase maturity [Line Items]
Securities Sold under Agreements to Repurchase	$ 1,503	$ 1,633
US Treasury Securities [Member]
securities sold under agreement to repurchase maturity [Line Items]
Securities Sold under Agreements to Repurchase	95	27
US Government Agencies Debt Securities [Member]
securities sold under agreement to repurchase maturity [Line Items]
Securities Sold under Agreements to Repurchase	116	312
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	829	844
Commercial Paper [Member]
securities sold under agreement to repurchase maturity [Line Items]
Securities Sold under Agreements to Repurchase	19	49
Corporate Debt Securities [Member]
securities sold under agreement to repurchase maturity [Line Items]
Securities Sold under Agreements to Repurchase	444	401
Maturity Overnight [Member]
securities sold under agreement to repurchase maturity [Line Items]
Securities Sold under Agreements to Repurchase	1,225	1,468
Maturity Overnight [Member] | US Treasury Securities [Member]
securities sold under agreement to repurchase maturity [Line Items]
Securities Sold under Agreements to Repurchase	95	27
Maturity Overnight [Member] | US Government Agencies Debt Securities [Member]
securities sold under agreement to repurchase maturity [Line Items]
Securities Sold under Agreements to Repurchase	101	288
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	694	793
Maturity Overnight [Member] | Commercial Paper [Member]
securities sold under agreement to repurchase maturity [Line Items]
Securities Sold under Agreements to Repurchase	19	49
Maturity Overnight [Member] | Corporate Debt Securities [Member]
securities sold under agreement to repurchase maturity [Line Items]
Securities Sold under Agreements to Repurchase	316	311
Maturity up to 30 days [Member]
securities sold under agreement to repurchase maturity [Line Items]
Securities Sold under Agreements to Repurchase	238	125
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	15	24
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	135	51
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	88	50
Maturity 30 to 90 Days [Member]
securities sold under agreement to repurchase maturity [Line Items]
Securities Sold under Agreements to Repurchase	40	40
Maturity 30 to 90 Days [Member] | US Treasury Securities [Member]
securities sold under agreement to repurchase maturity [Line Items]
Securities Sold under Agreements to Repurchase	0	0
Maturity 30 to 90 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 30 to 90 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	0
Maturity 30 to 90 Days [Member] | Commercial Paper [Member]
securities sold under agreement to repurchase maturity [Line Items]
Securities Sold under Agreements to Repurchase	0	0
Maturity 30 to 90 Days [Member] | Corporate Debt Securities [Member]
securities sold under agreement to repurchase maturity [Line Items]
Securities Sold under Agreements to Repurchase	$ 40	$ 40