Consolidated Statements of Changes in Stockholders' Equity - USD ($) $ in Millions	Total	Cumulative Effect, Period of Adoption, Adjustment		Adjusted Balance	Common Stock (Par Value: $0.01)	Preferred Stock (Par Value: $0.01)	Paid-in Capital in Excess of Par	Retained Earnings	Retained Earnings Cumulative Effect, Period of Adoption, Adjustment		Retained Earnings Adjusted Balance	Treasury Stock, at Cost	Accumulated Other Comprehensive Loss, Net of Tax
Balance at Dec. 31, 2019	$ 6,711	$ (10)	[1]	$ 6,701	$ 5	$ 503	$ 6,115	$ 342	$ (10)	[1]	$ 332	$ (221)	$ (33)
Balance, shares at Dec. 31, 2019					467,346,781
Accounting Standards Update [Extensible List]		us-gaap:AccountingStandardsUpdate201613Member							us-gaap:AccountingStandardsUpdate201613Member
Shares issued for restricted stock, net of forfeitures							(22)					22
Shares issued for restricted stock, net of forfeitures, shares					2,321,105
Compensation expense related to restricted stock awards	16						16
Net income	205							205
Dividends paid on common stock	(158)							(158)
Dividends paid on preferred stock	(16)							(16)
Purchase of common stock	(58)											(58)
Purchase of common stock, shares					(5,734,055)
Other comprehensive income (loss), net of tax	3												3
Balance at Jun. 30, 2020	6,693				$ 5	503	6,109	363				(257)	(30)
Balance, shares at Jun. 30, 2020					463,933,831
Balance at Mar. 31, 2020	6,637				$ 5	503	6,102	344				(236)	(81)
Balance, shares at Mar. 31, 2020					466,360,703
Compensation expense related to restricted stock awards	7						7
Net income	105							105
Dividends paid on common stock	(78)							(78)
Dividends paid on preferred stock	(8)							(8)
Purchase of common stock	(21)											(21)
Purchase of common stock, shares					(2,426,872)
Other comprehensive income (loss), net of tax	51												51
Balance at Jun. 30, 2020	6,693				$ 5	503	6,109	363				(257)	(30)
Balance, shares at Jun. 30, 2020					463,933,831
Balance at Dec. 31, 2020	$ 6,842				$ 5	503	6,123	494				(258)	(25)
Balance, shares at Dec. 31, 2020					463,901,808
Accounting Standards Update [Extensible List]	us-gaap:AccountingStandardsUpdate201613Member
Shares issued for restricted stock, net of forfeitures							(28)					28
Shares issued for restricted stock, net of forfeitures, shares					2,515,942
Compensation expense related to restricted stock awards	$ 16						16
Net income	297							297
Dividends paid on common stock	(158)							(158)
Dividends paid on preferred stock	(16)							(16)
Purchase of common stock	(15)											(15)
Purchase of common stock, shares					(1,360,788)
Other comprehensive income (loss), net of tax	(50)												(50)
Balance at Jun. 30, 2021	6,916				$ 5	503	6,111	617				(245)	(75)
Balance, shares at Jun. 30, 2021					465,056,962
Balance at Mar. 31, 2021	6,796				$ 5	503	6,103	552				(245)	(122)
Balance, shares at Mar. 31, 2021					465,074,384
Compensation expense related to restricted stock awards	8						8
Net income	152							152
Dividends paid on common stock	(79)							(79)
Dividends paid on preferred stock	(8)							(8)
Purchase of common stock, shares					(17,422)
Other comprehensive income (loss), net of tax	47												47
Balance at Jun. 30, 2021	$ 6,916				$ 5	$ 503	$ 6,111	$ 617				$ (245)	$ (75)
Balance, shares at Jun. 30, 2021					465,056,962

[1] Amount represents a $10 million cumulative adjustment, net of tax, to retained earnings as of January 1, 2020, as a result of the adoption of ASU 2016-13, Financial Instruments - Credit Losses (Topic 326): Measurement of Credit Losses on Financial Instruments, which became effective January 1, 2020.