Income Taxes Income Tax Rate Reconciliation (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Income Tax Rate Reconciliation [Line Items]
Income Tax Reconciliation, Income Tax Expense (Benefit), at Federal Statutory Income Tax Rate	$ 956	$ 254	$ 1
Effective Income Tax Rate Reconciliation, at Federal Statutory Income Tax Rate	35.00%	35.00%	35.00%	[1]
Income Tax Reconciliation, Tax Exempt Income	77	72	74
Effective Income Tax Rate Reconciliation, Tax Exempt Income	(2.80%)	(9.90%)
Income Tax Reconciliation, Deductions, Dividends	8	14	13
Effective Income Tax Rate Reconciliation, Deductions, Dividends	(0.30%)	(1.90%)
Income Tax Reconciliation, Tax Credits	83	88	88
Effective Income Tax Rate Reconciliation, Tax Credits	(3.00%)	(12.10%)
Income Tax Reconciliation, State and Local Income Taxes	(6)	2	12
Effective Income Tax Rate Reconciliation, State and Local Income Taxes	(0.20%)	0.20%
Income Tax Reconciliation, Tax Settlements	0	0	(20)
Effective Income Tax Rate Reconciliation, Tax Settlements	0.00%	0.00%
Income Tax Reconciliation, Other Adjustments	(9)	(3)	(3)
Effective Income Tax Rate Reconciliation, Other Adjustments	(0.40%)	(0.40%)
Income Tax Expense (Benefit)	$ 773	$ 79	$ (185)
Effective Income Tax Rate, Continuing Operations	28.30%	10.90%

[1] "NM" - Calculated percentage was not considered to be meaningful