Income Taxes Income Tax Rate Reconciliation (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Income Tax Rate Reconciliation [Line Items]
Effective Income Tax Rate Reconciliation at Federal Statutory Income Tax Rate, Amount		$ 698	$ 982	$ 939
Effective Income Tax Rate Reconciliation, at Federal Statutory Income Tax Rate, Percent		21.00%	35.00%	35.00%
Effective Income Tax Rate Reconciliation, State and Local Income Taxes, Amount		$ 85	$ 92	$ 59
Effective Income Tax Rate Reconciliation, State and Local Income Taxes, Percent		2.60%	3.30%	2.20%
Effective Income Tax Rate Reconciliation, Tax Exempt Income, Amount		$ (67)	$ (90)	$ (86)
Effective Income Tax Rate Reconciliation, Tax Exempt Income, Percent		(2.00%)	(3.20%)	(3.20%)
Effective Income Tax Rate Reconciliation, Tax Credit, Amount	[1]	$ (106)	$ (117)	$ (86)
Effective Income Tax Rate Reconciliation, Tax Credit, Percent	[1]	(3.20%)	(4.20%)	(3.20%)
Effective Income Tax Rate Reconciliation, Deferred Taxes Remeasurement, Amount		$ (55)	$ (303)	$ 0
Effective Income Tax Rate Reconciliation, Deferred Taxes Remeasurement, Percent		(1.70%)	(10.80%)	0.00%
Effective Income Tax Rate Reconciliation, Other Adjustments, Amount	[2]	$ (7)	$ (32)	$ (21)
Effective Income Tax Rate Reconciliation, Other Adjustments, Percent	[2]	(0.20%)	(1.10%)	(0.80%)
Income Tax Expense (Benefit)		$ 548	$ 532	$ 805
Effective Income Tax Rate Reconciliation, Percent		16.50%	19.00%	30.00%
Investments [Member]
Income Tax Rate Reconciliation [Line Items]
Effective Income Tax Rate Reconciliation, Tax Credit, Amount	[1]	$ (84)	$ (34)	$ (1)
Adjustments for New Accounting Principle, Early Adoption [Member]
Income Tax Rate Reconciliation [Line Items]
Effective Income Tax Rate Reconciliation, Deferred Taxes Remeasurement, Amount	[2]	$ 22	$ 25	$ 15

[1] Excludes income tax benefits of $84 million, $34 million, and $1 million for the years ended December 31, 2018, 2017, and 2016, respectively, related to tax credits, which were recognized as a reduction to the related investment asset.

[2] Includes excess tax benefits of $22 million, $25 million, and $15 million for the years ended December 31, 2018, 2017, and 2016, respectively, related to the Company's adoption of ASU 2016-09.