Income Taxes Income Tax Rate Reconciliation (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2016		Dec. 31, 2015	Dec. 31, 2014
Income Tax Rate Reconciliation [Line Items]
Effective Income Tax Rate Reconciliation at Federal Statutory Income Tax Rate, Amount		$ 939		$ 944	$ 793
Effective Income Tax Rate Reconciliation, at Federal Statutory Income Tax Rate, Percent		35.00%		35.00%	35.00%
Effective Income Tax Rate Reconciliation, State and Local Income Taxes, Amount		$ 53		$ 25	$ 12
Effective Income Tax Rate Reconciliation, State and Local Income Taxes, Percent		2.00%		0.90%	0.50%
Effective Income Tax Rate Reconciliation, Tax Exempt Income, Amount		$ (86)		$ (88)	$ (89)
Effective Income Tax Rate Reconciliation, Tax Exempt Income, Percent		(3.20%)		(3.30%)	(3.90%)
Effective Income Tax Rate Reconciliation, Change in UTBs, Amount		$ 6		$ (31)	$ (82)
Effective Income Tax Rate Reconciliation, Change in UTBs, Percent		0.20%		(1.10%)	(3.60%)
Effective Income Tax Rate Reconciliation, Tax Credit, Amount	[1]	$ (86)		$ (69)	$ (65)
Effective Income Tax Rate Reconciliation, Tax Credit, Percent	[1]	(3.20%)		(2.60%)	(2.90%)
Effective Income Tax Rate Reconciliation, Nondeductible Expense, Amount		$ 8		$ 0	$ 57
Effective Income Tax Rate Reconciliation, Nondeductible Expense, Percent		(0.30%)		(0.00%)	(2.50%)
Effective Income Tax Rate Reconciliation, Other Adjustments, Amount		$ (29)	[2]	$ (17)	$ (19)
Effective Income Tax Rate Reconciliation, Other Adjustments, Percent		(1.10%)	[2]	(0.60%)	(0.80%)
Income Tax Expense (Benefit)		$ 805		$ 764	$ 493
Effective Income Tax Rate Reconciliation, Percent		30.00%		28.30%	21.80%
Investments [Member]
Income Tax Rate Reconciliation [Line Items]
Effective Income Tax Rate Reconciliation, Tax Credit, Amount		$ (2)		$ (6)	$ (21)
Adjustments for New Accounting Principle, Early Adoption [Member]
Income Tax Rate Reconciliation [Line Items]
Effective Income Tax Rate Reconciliation, Other Adjustments, Amount	[2]	$ 15

[1] Excludes income tax benefits of $2 million, $6 million, and $21 million for the years ended December 31, 2016, 2015, and 2014, respectively, related to tax credits, which were recognized as a reduction to the related investment asset.

[2] Includes income tax benefits of $15 million related to the Company's early adoption of ASU 2016-09. See Note 1, "Significant Accounting Policies," for additional information.