Preferred Stock - Number of Shares Issued and Outstanding and Carrying Amount of Preferred Stock (Detail) (USD $) In Millions, except Share data, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012
Class of Stock [Line Items]
Shares Issued and Outstanding	159,910	159,910
Liquidation Preference	$ 4,936	$ 4,936
Discount	167	167
Carrying Amount	4,769	4,769
Series A [Member]
Class of Stock [Line Items]
Shares Issued and Outstanding	12,510	12,510
Liquidation Preference	1,251	1,251
Discount	145	145
Carrying Amount	1,106	1,106
Series B [Member]
Class of Stock [Line Items]
Shares Issued and Outstanding	40,000	40,000
Liquidation Preference	1,000	1,000
Carrying Amount	1,000	1,000
Series D [Member]
Class of Stock [Line Items]
Shares Issued and Outstanding	20,000	20,000
Liquidation Preference	500	500
Carrying Amount	500	500
Series F [Member]
Class of Stock [Line Items]
Shares Issued and Outstanding	44,000	44,000
Liquidation Preference	1,100	1,100
Discount	12	12
Carrying Amount	1,088	1,088
Series G [Member]
Class of Stock [Line Items]
Shares Issued and Outstanding	43,400	43,400
Liquidation Preference	1,085	1,085
Discount	10	10
Carrying Amount	$ 1,075	$ 1,075