Repurchase Agreements And Other Debt (Repurchase Arrangements And Weighted Average Interest Rates Classified By Original Maturities) (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011
Debt Instrument, Face Amount	$ 908	$ 54
Borrowings Outstanding	74,478	47,681
Average Interest Rate	0.51%	0.40%
Weighted Average Days to Maturity	118	51
1 Month or Less
Borrowings Outstanding	4,011	2,558
Average Interest Rate	0.48%	0.43%
Weighted Average Days to Maturity	13	10
thirty one to ninety [Member]
Borrowings Outstanding	28,307	24,518
Average Interest Rate	0.49%	0.39%
Weighted Average Days to Maturity	37	32
120 to 180 days [Member]
Borrowings Outstanding	24,303	16,475
Average Interest Rate	0.49%	0.37%
Weighted Average Days to Maturity	63	53
210 to 270 days [Member]
Borrowings Outstanding	5,222	2,423
Average Interest Rate	0.54%	0.45%
Weighted Average Days to Maturity	79	141
300 to 360 days [Member]
Borrowings Outstanding	7,813	1,006
Average Interest Rate	0.58%	0.53%
Weighted Average Days to Maturity	222	244
390 to 720 days [Member]
Borrowings Outstanding	1,917	600
Average Interest Rate	0.65%	0.51%
Weighted Average Days to Maturity	564	268
750 to 1080 days [Member]
Borrowings Outstanding	2,803
Average Interest Rate	0.69%
Weighted Average Days to Maturity	963
Greater than 1080 days [Member]
Borrowings Outstanding	102
Average Interest Rate	0.73%
Weighted Average Days to Maturity	1,751
Mortgage Backed Securities, Other [Member]
Borrowings Outstanding	74,478	47,580
Average Interest Rate	0.51%	0.40%
Weighted Average Days to Maturity	118	51
Treasuries [Member]
Borrowings Outstanding		$ 101
Average Interest Rate		0.40%
Weighted Average Days to Maturity		1