Other Assets-Seed Capital and Private Equity Investments Valued Using Net Asset Value (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended		12 Months Ended
	Mar. 31, 2013		Dec. 31, 2012
Deferred Costs, Capitalized, Prepaid, and Other Assets Disclosure [Line Items]
Fair value	$ 256		$ 252
Unfunded commitments	41		44
Private Equity Funds
Deferred Costs, Capitalized, Prepaid, and Other Assets Disclosure [Line Items]
Fair value	88	[1]	99	[1]
Unfunded commitments	12	[1]	13	[1]
Other Funds
Deferred Costs, Capitalized, Prepaid, and Other Assets Disclosure [Line Items]
Fair value	168	[2]	153	[2]
Unfunded commitments	$ 29	[2]	$ 31	[2]
Redemption frequency	Monthly-yearly	[2]	Monthly-yearly	[2]
Redemption notice period	3-45 days	[2]	3-45 days	[2]

[1] Private equity funds primarily include numerous venture capital funds that invest in various sectors of the economy. Private equity funds do not have redemption rights. Distributions from such funds will be received as the underlying investments in the funds are liquidated.

[2] Other funds include various market neutral, leveraged loans, hedge funds, real estate and structured credit funds. Redemption notice periods vary by fund.