Condensed Financial Information (Parent Company) (Interest Expense) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Interest Expense [Abstract]
Total interest expense	$ 827	$ 841	$ 874
Parent Company
Interest Expense [Abstract]
Total interest expense	1,009	1,108	1,152
Parent Company | Long-term Debt
Interest Expense [Abstract]
Total interest expense	755	774	811
Parent Company | Long-term Debt | Affiliated Entity [Member]
Interest Expense [Abstract]
Total interest expense	45	112	160
Parent Company | Secured Debt [Member]
Interest Expense [Abstract]
Total interest expense	6	27	47
Parent Company | Junior Subordinated Debt [Member]
Interest Expense [Abstract]
Total interest expense	$ 203	$ 195	$ 134