Accumulated Other Comprehensive Income (Details) - USD ($) $ in Millions		3 Months Ended		6 Months Ended
		Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Accumulated Other Comprehensive Income (Loss), Beginning of period				$ 51
Net change in fair value		$ (10)	$ (2)	(19)	$ (18)
Noncredit other-than-temporary impairment losses		2	1	3	1
Amortization of pension and posttretirement		0	1	1	2
Total other comprehensive income (loss)		(8)	0	(15)	(15)
Accumulated Other Comprehensive Income (Loss), End of period		36		36
Pension and Postretirement Benefits [Member]
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Accumulated Other Comprehensive Income (Loss), Beginning of period		(20)	(23)	(21)	(24)
Net change in fair value		0	0	0	0
Noncredit other-than-temporary impairment losses		0	0	0	0
Amortization of pension and posttretirement	[1]	0	1	1	2
Total other comprehensive income (loss)		0	1	1	2
Accumulated Other Comprehensive Income (Loss), End of period		(20)	(22)	(20)	(22)
Total Accumulated Other Comprehensive Income (Loss) [Member]
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Accumulated Other Comprehensive Income (Loss), Beginning of period		44	95	51	110
Net change in fair value		(10)	(2)	(19)	(18)
Noncredit other-than-temporary impairment losses		2	1	3	1
Amortization of pension and posttretirement	[1]	0	1	1	2
Total other comprehensive income (loss)		(8)	0	(15)	(15)
Accumulated Other Comprehensive Income (Loss), End of period		36	95	36	95
Available-for-sale Securities [Member] | Noncredit Portion of Other Than Temporary Impairment Losses on Available for Sale Securities [Member]
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Accumulated Other Comprehensive Income (Loss), Beginning of period		64	118	72	134
Net change in fair value		(10)	(2)	(19)	(18)
Noncredit other-than-temporary impairment losses		2	1	3	1
Amortization of pension and posttretirement	[1]	0	0	0	0
Total other comprehensive income (loss)		(8)	(1)	(16)	(17)
Accumulated Other Comprehensive Income (Loss), End of period		$ 56	$ 117	$ 56	$ 117

[1] Included in Noninterest expense - Other on the Statements of Income