Investment Securities (Parenthetical) (Details) (USD $) In Millions, unless otherwise specified	Sep. 30, 2012	Dec. 31, 2011
Investment [Line Items]
Investment securities (Note 3)	$ 48,695	$ 47,359
OTTI previously recognized through OCI on securities held	(137)
Residential Mortgage Backed Securities [Member] | Mortgage-backed Securities, Issued by Private Enterprises [Member]
Investment [Line Items]
Investment securities (Note 3)	895
Residential Mortgage Backed Securities [Member] | Mortgage-backed Securities, Issued by US Government Sponsored Enterprises [Member]
Investment [Line Items]
Investment securities (Note 3)	$ 1,529