Organization, Basis of Presentation and Summary of Significant Accounting Policies (Details) $ in Millions	3 Months Ended			6 Months Ended
	Jun. 30, 2017 USD ($)	Mar. 31, 2017 USD ($)	Jun. 30, 2016 USD ($)	Jun. 30, 2017 USD ($)	Jun. 30, 2016 USD ($)
Cumulative-effect adjustment to equity				$ 3
Income tax expense (benefit)	$ 124		$ 81	$ 204	$ 122
Prospective Adoption of New Accounting Pronouncements [Abstract]
Number of regional branches	30			30
Accounting standards update 2016-09
Deferred tax asset		$ 3
Cumulative-effect adjustment to equity		$ 3
Prior period reclassification adjustment					$ 13
Income tax expense (benefit)				$ (6)