CONSOLIDATED STATEMENT OF CHANGES IN EQUITY - USD ($) $ in Millions	Total	Preferred Stock [Member]	Common Stock [Member]	Additional Paid-in Capital [Member]	Retained Earnings [Member]	Accumulated Other Comprehensive Loss [Member]	As Previously Reported [Member] Retained Earnings [Member]	As Previously Reported [Member] Accumulated Other Comprehensive Loss [Member]
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Cumulative effect of new accounting principle in period of adoption | Accounting Standards Update 2016-02 [Member]					$ 0
Cumulative effect of new accounting principle in period of adoption | Accounting Standards Update 2016-01, Equity Investments Previously Classified as Available-for-sale [Member]					(4)	$ 4
Cumulative effect of new accounting principle in period of adoption | Accounting Standards Update 2016-01, Equity Investments Previously Measured at Cost [Member]					10
Cumulative effect of new accounting principle in period of adoption | Accounting Standards Update 2018-02 [Member]					91	(91)
Balance at beginning of period at Dec. 31, 2017		$ 1,265
Balance at beginning of period at Dec. 31, 2017			$ 0	$ 18,130	1,227	(518)	$ 1,130	$ (431)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Return of capital to parent				0
Employee benefit plans				6
Net income (loss)	$ 208				208
Cash dividends declared on preferred stock					(38)
Other comprehensive income (loss), net of tax	(280)					(280)
Balance at end of period at Sep. 30, 2018	18,735		0	18,136	1,397	(798)
Balance at end of period at Sep. 30, 2018	20,000	1,265
Balance at beginning of period at Jun. 30, 2018		1,265
Balance at beginning of period at Jun. 30, 2018			0	18,135	1,221	(636)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Employee benefit plans				1
Net income (loss)	177				177
Cash dividends declared on preferred stock					(1)
Other comprehensive income (loss), net of tax	(162)					(162)
Balance at end of period at Sep. 30, 2018	18,735		0	18,136	1,397	(798)
Balance at end of period at Sep. 30, 2018	20,000	1,265
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Cumulative effect of new accounting principle in period of adoption | Accounting Standards Update 2016-02 [Member]					27
Cumulative effect of new accounting principle in period of adoption | Accounting Standards Update 2016-01, Equity Investments Previously Classified as Available-for-sale [Member]					0	0
Cumulative effect of new accounting principle in period of adoption | Accounting Standards Update 2016-01, Equity Investments Previously Measured at Cost [Member]					0
Cumulative effect of new accounting principle in period of adoption | Accounting Standards Update 2018-02 [Member]					0	0
Balance at beginning of period at Dec. 31, 2018	20,506	1,265
Balance at beginning of period at Dec. 31, 2018	19,241		0	18,136	1,498	(366)	$ 1,471
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Return of capital to parent				(2,400)
Employee benefit plans				0
Net income (loss)	(20)				(20)
Cash dividends declared on preferred stock					(38)
Other comprehensive income (loss), net of tax	383					383
Balance at end of period at Sep. 30, 2019	17,193		0	15,736	1,440	17
Balance at end of period at Sep. 30, 2019	18,458	1,265
Balance at beginning of period at Jun. 30, 2019		1,265
Balance at beginning of period at Jun. 30, 2019			0	15,734	1,690	(55)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Employee benefit plans				2
Net income (loss)	(250)				(250)
Cash dividends declared on preferred stock					0
Other comprehensive income (loss), net of tax	72					72
Balance at end of period at Sep. 30, 2019	17,193		$ 0	$ 15,736	$ 1,440	$ 17
Balance at end of period at Sep. 30, 2019	$ 18,458	$ 1,265