Organization, Basis of Presentation and Summary of Significant Accounting Policies (Details - Adoption of New Accounting Standards) $ in Millions	3 Months Ended	12 Months Ended
	Mar. 31, 2017 USD ($)	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)
Deferred tax asset		$ 659	$ 1,309
Cumulative-effect adjustment to equity		3
Income tax expense (benefit)		$ 450	286	$ (177)
Prospective Adoption of New Accounting Pronouncements [Abstract]
Number of regional branches		30
Number of corporate locations		8
Accounting standards update 2016-09
Deferred tax asset	$ 3
Cumulative-effect adjustment to equity	$ 3
Prior period reclassification adjustment			$ 21	$ 11
Income tax expense (benefit)		$ (7)
Adjustments for new accounting principle, early adoption [Member]
Cumulative-effect adjustment to equity		7
Fair value of agency securities transferred		4,700
Net gain recognized within other comprehensive income for transferred securities		7
Increase to retained earnings		$ 14