Condensed Financial Information (Parent Company) (Interest Expense) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Interest Expense [Abstract]
Total interest expense	$ 632	$ 656	$ 827
Parent Company
Interest Expense [Abstract]
Total interest expense	833	850	1,009
Parent Company | Long-term Debt
Interest Expense [Abstract]
Total interest expense	570	591	755
Parent Company | Long-term Debt | Affiliated Entity [Member]
Interest Expense [Abstract]
Total interest expense	52	48	45
Parent Company | Secured Debt [Member]
Interest Expense [Abstract]
Total interest expense	6	6	6
Parent Company | Junior Subordinated Debt [Member]
Interest Expense [Abstract]
Total interest expense	$ 205	$ 205	$ 203