Derivative Instruments and Hedging Activities (Narrative) (Details) - USD ($) $ in Millions	Sep. 30, 2016	Dec. 31, 2015
Forward Contract Indexed to Issuer's Equity [Line Items]
Derivative, Notional Amount	$ 38,379	$ 59,116
Cash Collateral Placed with Counterparties Excluding Cash Collateral Associated with Repurchase Agreements	70	103
Securities Collateral Placed with Counterparties	49	86
Non-derivative Cash Collateral Placed with Counterparties Associated with the Repurchase Agreements	7	21
Cash Collateral Received from Counterparties, Excluding Collateral Associated with Repurchase Agreements	113	82
Non-cash collateral received	2	7
Designated as Hedging Instrument [Member]
Forward Contract Indexed to Issuer's Equity [Line Items]
Derivative, Notional Amount	6,975	14,340
Designated as Hedging Instrument [Member] | Equity Contract [Member]
Forward Contract Indexed to Issuer's Equity [Line Items]
Derivative, Notional Amount	17	32
Designated as Hedging Instrument [Member] | Forward Contracts [Member] | Equity Contract [Member]
Forward Contract Indexed to Issuer's Equity [Line Items]
Derivative, Notional Amount	$ 17	$ 32