Derivative Financial Instruments (Income Statement Relationship of Fair Value and Cash Flow Hedging) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Interest Expense [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Total expense from the effects of fair value or cash flow hedges	$ (188)	$ (150)	$ (564)	$ (575)
Net Realized Investments Gain Loss [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Total income from the effects of fair value or cash flow hedges	27	115	5	138
Interest Rate Swaps [Member] | Interest Expense [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Change in Unrealized Gain (Loss) on Fair Value Hedging Instruments	0	0	1	0
Interest Rate Swaps [Member] | Net Realized Investments Gain Loss [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Change in Unrealized Gain (Loss) on Fair Value Hedging Instruments	0		0
Forward Starting Pay Fixed Swaps [Member] | Interest Expense [Member] | Cash Flow Hedging [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Hedge (loss) gain reclassified from accumulated other comprehensive loss	(4)	(2)	(10)	(5)
Forward Starting Pay Fixed Swaps [Member] | Net Realized Investments Gain Loss [Member] | Cash Flow Hedging [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Hedge (loss) gain reclassified from accumulated other comprehensive loss	0	0		(12)
Fixed Rate Debt [Member] | Interest Expense [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Change in Unrealized Gain (Loss) on Hedged Item in Fair Value Hedge	0	$ 0	(1)	$ 0
Fixed Rate Debt [Member] | Net Realized Investments Gain Loss [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Change in Unrealized Gain (Loss) on Hedged Item in Fair Value Hedge	$ 0		$ 0