Income Taxes (Reconciliation between the Company's federal income tax (expense) benefit at statutory rates and the recorded income tax (expense) benefit) (Details) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Effective Income Tax Rate Reconciliation, Amount [Abstract]
Income tax expense at statutory rates		$ (459)	$ (398)	$ (192)
Tax benefit from tax exempt income		131	124	123
Foreign taxes and credits		3	3	9
Net deferred tax asset remeasurement	$ (83)	(83)	0	0
Other tax expense		(3)	(7)	(10)
Income tax expense		$ (411)	$ (278)	$ (70)