Consolidated Statement of Stockholders' Equity (USD $) In Millions, except Share data, unless otherwise specified	Total	Preferred Stock [Member]	Common Stock [Member]	Additional Paid-in Capital [Member]	Retained Earnings (Accumulated Deficit) [Member]	Accumulated Other Comprehensive Income (Loss) [Member]	Interest Rate Swap [Member]
Balance, value at Dec. 31, 2009	$ 547	$ 0	$ 0	$ 507	$ 20	$ 20
Balance, Common Stock, shares at Dec. 31, 2009			24,300,000
Balance, Preferred Stock, shares at Dec. 31, 2009		0
Net income	288				288
Other comprehensive income (loss):
Unrealized gain (loss) on available-for-sale securities, net	(64)					(64)
Unrealized (loss) gain on derivative instruments, net	(24)						(24)
Issuance of common stock, value	1,056		1	1,055
Payments for Repurchase of Common Stock	0
Issuance of common stock, shares	28,400,000		40,600,000
Common dividends declared	230		(230)		230
Proceeds from Issuance of Preferred Stock and Preference Stock	0
Balance, value at Dec. 31, 2010	1,573	0	1	1,562	78	(68)
Balance, Common Stock, shares at Dec. 31, 2010			64,900,000
Balance, Preferred Stock, shares at Dec. 31, 2010		0
Net income	770				770
Other comprehensive income (loss):
Unrealized gain (loss) on available-for-sale securities, net	1,029					1,029
Unrealized (loss) gain on derivative instruments, net	(650)						(650)
Unrealized (loss) gain on derivative instruments, net (Discontinuation of Election to Account for Interest Rate Swaps as Designated Cash Flow Hedges [Member])							54
Preferred Stock, Shares Issued	0
Issuance of common stock, value	4,376		1	4,375
Payments for Repurchase of Common Stock	0
Issuance of common stock, shares	149,300,000		159,300,000
Common dividends declared	886		(886)		886
Proceeds from Issuance of Preferred Stock and Preference Stock	0
Balance, value at Dec. 31, 2011	6,212	0	2	5,937	(38)	311
Balance, Common Stock, shares at Dec. 31, 2011	224,200,000		224,200,000
Balance, Preferred Stock, shares at Dec. 31, 2011	0	0
Net income	1,277
Other comprehensive income (loss):
Unrealized gain (loss) on available-for-sale securities, net	1,039					1,039
Unrealized (loss) gain on derivative instruments, net	205
Unrealized (loss) gain on derivative instruments, net (Discontinuation of Election to Account for Interest Rate Swaps as Designated Cash Flow Hedges [Member])							205
Preferred Stock, Shares Issued	6,900,000
Issuance of common stock, value	3,601		1	3,600
Stock Repurchased During Period, Shares	(2,700,000)
Payments for Repurchase of Common Stock	77
Stock Repurchased During Period, Value	(77)
Dividends, Preferred Stock	(10)
Issuance of common stock, shares	108,000,000		117,400,000
Common dividends declared	1,518		(1,518)		1,518
Proceeds from Issuance of Preferred Stock and Preference Stock	167
Balance, value at Dec. 31, 2012	10,896	167	3	9,460	(289)	1,555
Balance, Common Stock, shares at Dec. 31, 2012	338,900,000		338,900,000
Balance, Preferred Stock, shares at Dec. 31, 2012	6,900,000	6,900,000
Balance, value at Sep. 30, 2012
Net income	810
Other comprehensive income (loss):
Unrealized gain (loss) on available-for-sale securities, net						(734)
Unrealized (loss) gain on derivative instruments, net (Discontinuation of Election to Account for Interest Rate Swaps as Designated Cash Flow Hedges [Member])							50
Preferred Stock, Shares Issued	6,900,000
Balance, value at Dec. 31, 2012	$ 10,896	$ 167				$ 1,555
Balance, Common Stock, shares at Dec. 31, 2012	338,900,000
Balance, Preferred Stock, shares at Dec. 31, 2012	6,900,000	6,900,000