Consolidated Statement of Changes in Equity - USD ($) $ in Millions	Total	Total	Common Shares	Common Stock and Capital Surplus	Retained Earnings	Accumulated Other Comprehensive Inc. (Loss)	Noncontrolling Interests	Redeemable noncontrolling interests
Beginning Balance, shares at Dec. 31, 2016			86,924,399
Beginning Balance at Dec. 31, 2016	$ 4,919	$ 4,916		$ 1,198	$ 3,343	$ 375	$ 3
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss) attributable to parent	475	475			475
Net income (loss), including portion attributable to nonredeemable noncontrolling interest	477						2
Other comprehensive income (loss)	296	296				296	0
Impact of the U.S. corporate tax rate change on AOCI	0	0			(145)	145	0
Dividends	(421)	(421)			(421)
Shares issued:
Exercise of stock options, shares			1,020,986
Exercise of stock options	34	34		34
Restricted stock awards, shares			232,250
Restricted stock awards	0	0		0
Other benefit plans, shares			99,588
Other benefit plans	10	10		10
Dividend reinvestment plan, shares			42,572
Dividend reinvestment plan	4	4		4
Stock-based compensation: Expense	24	24		24
Shares exchanged — benefit plans, shares			(37,718)
Shares exchanged — benefit plans	(5)	(5)		(1)	(4)
Forfeitures of restricted stock, shares			(6,617)
Forfeitures of restricted stock	0	0		0
Sale of redeemable noncontrolling interests	(3)	(3)				(3)		$ 3
Other	(4)				0		(4)
Ending Balance, shares at Dec. 31, 2017			88,275,460
Ending Balance at Dec. 31, 2017	5,331	5,330		1,269	3,248	813	1
Beginning Balance, Redeemable Noncontrolling Interests at Dec. 31, 2016	0
Redeemable Noncontrolling Interest, Equity, Carrying Amount [Abstract]
Sale of redeemable noncontrolling interests	(3)	(3)				(3)		$ 3
Other	0
Ending Balance, Redeemable Noncontrolling Interests at Dec. 31, 2017	3
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss) attributable to parent	530	530			530
Net income (loss), including portion attributable to nonredeemable noncontrolling interest	531						1
Other comprehensive income (loss)	(544)	(544)				(544)	0
Dividends	(397)	(397)			(397)
Shares issued:
Exercise of stock options, shares			778,270
Exercise of stock options	29	29		29
Restricted stock awards, shares			200,625
Restricted stock awards	0	0		0
Other benefit plans, shares			103,797
Other benefit plans	12	12		12
Dividend reinvestment plan, shares			29,998
Dividend reinvestment plan	3	3		3
Stock-based compensation: Expense	23	23		23
Shares acquired and retired, shares			(65,589)
Shares acquired and retired	(6)	(6)		(1)	(5)
Shares exchanged — benefit plans, shares			(26,520)
Shares exchanged — benefit plans	(3)	(3)		(1)	(2)
Forfeitures of restricted stock, shares			(4,317)
Forfeitures of restricted stock	0	0		0
Other	$ (11)	(11)			(11)	0	0
Ending Balance, shares at Dec. 31, 2018	89,291,724		89,291,724
Ending Balance at Dec. 31, 2018	$ 4,972	4,970		1,334	3,588	48	2
Redeemable Noncontrolling Interest, Equity, Carrying Amount [Abstract]
Net income (loss) attributable to redeemable noncontrolling interest	(14)
Other	11
Ending Balance, Redeemable Noncontrolling Interests at Dec. 31, 2018	0
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss) attributable to parent	897	897			897
Net income (loss), including portion attributable to nonredeemable noncontrolling interest	895						(2)
Other comprehensive income (loss)	815	815				815	0
Dividends	$ (446)	(446)			(446)
Shares issued:
Exercise of stock options, shares	747,167		747,167
Exercise of stock options	$ 31	31		31
Restricted stock awards, shares			232,635
Restricted stock awards	0	0		0
Other benefit plans, shares			77,429
Other benefit plans	8	8		8
Dividend reinvestment plan, shares			19,334
Dividend reinvestment plan	2	2		2
Stock-based compensation: Expense	23	23		23
Shares exchanged — benefit plans, shares			(50,062)
Shares exchanged — benefit plans	(5)	(5)		(1)	(4)
Forfeitures of restricted stock, shares			(14,541)
Forfeitures of restricted stock	0	0		0
Other	$ (26)	(26)			(26)		0
Ending Balance, shares at Dec. 31, 2019	90,303,686		90,303,686
Ending Balance at Dec. 31, 2019	$ 6,269	$ 6,269		$ 1,397	$ 4,009	863	$ 0
Redeemable Noncontrolling Interest, Equity, Carrying Amount [Abstract]
Net income (loss) attributable to redeemable noncontrolling interest	(26)
Other	26
Ending Balance, Redeemable Noncontrolling Interests at Dec. 31, 2019	$ 0
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Cumulative effect of accounting change						$ 0