Derivative Financial Instruments Derivative Financial Instruments (Income Statement Relationship of Fair Value and Cash Flow Hedging) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Net realized gains (losses) on financial instruments	$ 182	$ 67	$ (206)
Interest Expense [Member]
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Total expense from the effects of fair value or cash flow hedges	(784)	(746)	(753)
Forward Starting Pay Fixed Swaps [Member] | Interest Expense [Member] | Cash Flow Hedging [Member]
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Hedge (loss) gain reclassified from accumulated other comprehensive loss	(15)	(15)	(14)
Swap [Member] | Interest Expense [Member]
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Change in Unrealized Gain (Loss) on Hedged Item in Fair Value Hedge	(15)	2	0
Change in Unrealized Gain (Loss) on Fair Value Hedging Instruments	$ 15	$ (2)	$ 0