ESOP Preferred Stock (Details) - USD ($) $ / shares in Units, $ in Millions	6 Months Ended	12 Months Ended
	Jun. 30, 2019	Dec. 31, 2018
Class of Stock [Line Items]
Additional paid-in capital included related to preferred stock	$ 78	$ 95
Detail of Employee Stock Ownership Plan Preferred Stock [Abstract]
Shares issued and outstanding	1,213,418	1,406,460
Carrying value	$ 1,214	$ 1,407
Unearned ESOP shares	$ (1,292)	$ (1,502)
Employee Stock Ownership Plan Preferred Stock 2018 [Member]
Detail of Employee Stock Ownership Plan Preferred Stock [Abstract]
Shares issued and outstanding	336,945	336,945
Carrying value	$ 337	$ 337
Employee Stock Ownership Plan Preferred Stock 2018 [Member] | Minimum [Member]
Detail of Employee Stock Ownership Plan Preferred Stock [Abstract]
Adjustable dividend rate	7.00%	7.00%
Employee Stock Ownership Plan Preferred Stock 2018 [Member] | Maximum [Member]
Detail of Employee Stock Ownership Plan Preferred Stock [Abstract]
Adjustable dividend rate	8.00%	8.00%
Employee Stock Ownership Plan Preferred Stock 2017 [Member]
Detail of Employee Stock Ownership Plan Preferred Stock [Abstract]
Shares issued and outstanding	222,210	222,210
Carrying value	$ 222	$ 222
Employee Stock Ownership Plan Preferred Stock 2017 [Member] | Minimum [Member]
Detail of Employee Stock Ownership Plan Preferred Stock [Abstract]
Adjustable dividend rate	7.00%	7.00%
Employee Stock Ownership Plan Preferred Stock 2017 [Member] | Maximum [Member]
Detail of Employee Stock Ownership Plan Preferred Stock [Abstract]
Adjustable dividend rate	8.00%	8.00%
Employee Stock Ownership Plan Preferred Stock 2016 [Member]
Detail of Employee Stock Ownership Plan Preferred Stock [Abstract]
Shares issued and outstanding	227,450	233,835
Carrying value	$ 228	$ 234
Employee Stock Ownership Plan Preferred Stock 2016 [Member] | Minimum [Member]
Detail of Employee Stock Ownership Plan Preferred Stock [Abstract]
Adjustable dividend rate	9.30%	9.30%
Employee Stock Ownership Plan Preferred Stock 2016 [Member] | Maximum [Member]
Detail of Employee Stock Ownership Plan Preferred Stock [Abstract]
Adjustable dividend rate	10.30%	10.30%
Employee Stock Ownership Plan Preferred Stock 2015 [Member]
Detail of Employee Stock Ownership Plan Preferred Stock [Abstract]
Shares issued and outstanding	116,784	144,338
Carrying value	$ 117	$ 144
Employee Stock Ownership Plan Preferred Stock 2015 [Member] | Minimum [Member]
Detail of Employee Stock Ownership Plan Preferred Stock [Abstract]
Adjustable dividend rate	8.90%	8.90%
Employee Stock Ownership Plan Preferred Stock 2015 [Member] | Maximum [Member]
Detail of Employee Stock Ownership Plan Preferred Stock [Abstract]
Adjustable dividend rate	9.90%	9.90%
Employee Stock Ownership Plan Preferred Stock 2014 [Member]
Detail of Employee Stock Ownership Plan Preferred Stock [Abstract]
Shares issued and outstanding	136,151	174,151
Carrying value	$ 136	$ 174
Employee Stock Ownership Plan Preferred Stock 2014 [Member] | Minimum [Member]
Detail of Employee Stock Ownership Plan Preferred Stock [Abstract]
Adjustable dividend rate	8.70%	8.70%
Employee Stock Ownership Plan Preferred Stock 2014 [Member] | Maximum [Member]
Detail of Employee Stock Ownership Plan Preferred Stock [Abstract]
Adjustable dividend rate	9.70%	9.70%
Employee Stock Ownership Plan Preferred Stock 2013 [Member]
Detail of Employee Stock Ownership Plan Preferred Stock [Abstract]
Shares issued and outstanding	97,948	133,948
Carrying value	$ 98	$ 134
Employee Stock Ownership Plan Preferred Stock 2013 [Member] | Minimum [Member]
Detail of Employee Stock Ownership Plan Preferred Stock [Abstract]
Adjustable dividend rate	8.50%	8.50%
Employee Stock Ownership Plan Preferred Stock 2013 [Member] | Maximum [Member]
Detail of Employee Stock Ownership Plan Preferred Stock [Abstract]
Adjustable dividend rate	9.50%	9.50%
Employee Stock Ownership Plan Preferred Stock 2012 [Member]
Detail of Employee Stock Ownership Plan Preferred Stock [Abstract]
Shares issued and outstanding	49,134	77,634
Carrying value	$ 49	$ 78
Employee Stock Ownership Plan Preferred Stock 2012 [Member] | Minimum [Member]
Detail of Employee Stock Ownership Plan Preferred Stock [Abstract]
Adjustable dividend rate	10.00%	10.00%
Employee Stock Ownership Plan Preferred Stock 2012 [Member] | Maximum [Member]
Detail of Employee Stock Ownership Plan Preferred Stock [Abstract]
Adjustable dividend rate	11.00%	11.00%
Employee Stock Ownership Plan Preferred Stock 2011 [Member]
Detail of Employee Stock Ownership Plan Preferred Stock [Abstract]
Shares issued and outstanding	26,796	61,796
Carrying value	$ 27	$ 62
Employee Stock Ownership Plan Preferred Stock 2011 [Member] | Minimum [Member]
Detail of Employee Stock Ownership Plan Preferred Stock [Abstract]
Adjustable dividend rate	9.00%	9.00%
Employee Stock Ownership Plan Preferred Stock 2011 [Member] | Maximum [Member]
Detail of Employee Stock Ownership Plan Preferred Stock [Abstract]
Adjustable dividend rate	10.00%	10.00%
Employee Stock Ownership Plan Preferred Stock 2010 [Member]
Detail of Employee Stock Ownership Plan Preferred Stock [Abstract]
Shares issued and outstanding	0	21,603
Carrying value	$ 0	$ 22
Employee Stock Ownership Plan Preferred Stock 2010 [Member] | Minimum [Member]
Detail of Employee Stock Ownership Plan Preferred Stock [Abstract]
Adjustable dividend rate	9.50%	9.50%
Employee Stock Ownership Plan Preferred Stock 2010 [Member] | Maximum [Member]
Detail of Employee Stock Ownership Plan Preferred Stock [Abstract]
Adjustable dividend rate	10.50%	10.50%
Stock Compensation Plan [Member] | Convertible Preferred Stock [Member]
Class of Stock [Line Items]
Preferred stock, redemption price per share	$ 1,000