Concentrations - Portfolio Carrying Value by Geographical Area (Detail) (USD $) In Millions, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011
Entity Wide Disclosure On Geographic Areas Operations [Line Items]
Carrying Value	$ 4,066	$ 4,315
Total Portfolio	100.00%	100.00%
United States [Member]
Entity Wide Disclosure On Geographic Areas Operations [Line Items]
Carrying Value	2,755	3,186
Total Portfolio	67.70%	73.80%
Europe [Member]
Entity Wide Disclosure On Geographic Areas Operations [Line Items]
Carrying Value	629	693
Total Portfolio	15.50%	16.10%
Asia/Australia [Member]
Entity Wide Disclosure On Geographic Areas Operations [Line Items]
Carrying Value	505	241
Total Portfolio	12.40%	5.60%
Latin America [Member]
Entity Wide Disclosure On Geographic Areas Operations [Line Items]
Carrying Value	39	79
Total Portfolio	1.00%	1.80%
Other [Member]
Entity Wide Disclosure On Geographic Areas Operations [Line Items]
Carrying Value	$ 138	$ 116
Total Portfolio	3.40%	2.70%