Condensed Financial Information (Parent Only) (Details - Condensed Statement of Cash Flows) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Condensed Financial Statements, Captions [Line Items]
Net income	$ 172	$ 274	$ 219	$ 290	$ 270	$ 285	$ 250	$ 247	$ 955	$ 1,052	$ 614
Depreciation and amortization									225	244	262
Equity in undistributed (income) loss from subsidiaries									(6)	(9)	12
Losses on early extinguishment of debt									0	4	58
Other									15	18	(7)
Capital expenditures for property and equipment									(149)	(112)	(102)
Other									(34)	(25)	(43)
Proceeds from issuance of senior notes									0	420	999
Payments on senior notes									0	0	(1,049)
Proceeds from issuance of preferred stock									0	0	300
Repurchases of common stock									(1,085)	(1,139)	(362)
Preferred stock dividends									(40)	(36)	(25)
Common stock dividends									(135)	(36)	0
Other									(23)	(32)	(36)
Cash and equivalents	750				2,333				750	2,333	931
Parent Company [Member]
Condensed Financial Statements, Captions [Line Items]
Net income									955	1,052	614
Depreciation and amortization									74	55	51
Equity in undistributed (income) loss from subsidiaries									432	(216)	(573)
Losses on early extinguishment of debt									0	0	58
Other									189	292	213
Net Cash Provided by (Used in) Operating Activities, Continuing Operations									1,650	1,183	363
Capital expenditures for property and equipment									(87)	(60)	(59)
Cash contributions to subsidiaries									(31)	(464)	(61)
Other									0	2	6
Net Cash Provided by (Used in) Investing Activities, Continuing Operations									(118)	(522)	(114)
Proceeds from issuance of senior notes									0	420	999
Payments on senior notes									0	0	(1,049)
Proceeds from issuance of preferred stock									0	0	300
Repurchases of common stock									(1,085)	(1,139)	(362)
Preferred stock dividends									(40)	(36)	(25)
Common stock dividends									(135)	(36)	0
Other									2	(23)	(35)
Net Cash Provided by (Used in) Financing Activities, Continuing Operations									(1,258)	(814)	(172)
Cash and Cash Equivalents, Period Increase (Decrease)									274	(153)	77
Cash and equivalents	$ 614				$ 340				$ 614	$ 340	$ 493	$ 416