Fair Value of Financial Instruments (Narrative) (Details) - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets measured at fair value	$ 233,897	$ 245,265
Liabilities measured at fair value	1,793	3,689
Maximum [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value, Assets, Level 1 to Level 2 Transfers, Amount	1	1
Fair Value, Assets, Level 2 to Level 1 Transfers, Amount	1	1
Fair Value, Liabilities, Level 1 to Level 2 Transfers, Amount	1	1
Fair Value, Liabilities, Level 2 to Level 1 Transfers, Amount	$ 1	$ 1	$ 1