Fair Value of Financial Instruments (Redemption Of The Plan's Level 3 Investments) (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
MS IFHF SVP LP Cayman [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Liquidation Period (in years)		4 years
MS IFHF SVP LP Alpha [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Liquidation Period (in years)		4 years
RII World Timberfund, LLC [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Liquidation Period (in years)		10 years
Interest in Limited Partnerships and Limited Liability Companies [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value		$ 118	$ 92	$ 103
Interest in Limited Partnerships and Limited Liability Companies [Member] | MS IFHF SVP LP Cayman [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value	[1]	$ 1
Redemption Frequency	[1]	Through liquidation of underlying investments
Interest in Limited Partnerships and Limited Liability Companies [Member] | MS IFHF SVP LP Alpha [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value	[1]	$ 1
Redemption Frequency	[1]	Through liquidation of underlying investments
Interest in Limited Partnerships and Limited Liability Companies [Member] | RII World Timberfund, LLC [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value	[2]	$ 6
Redemption Frequency	[2]	Through liquidation of underlying investments
Interest in Limited Partnerships and Limited Liability Companies [Member] | E Casino Road, LLC (member)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value		$ 15
Redemption Frequency		Through liquidation of underlying investments
Interest in Limited Partnerships and Limited Liability Companies [Member] | Comm Drive, LLC [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value	[3]	$ 9
Redemption Frequency	[3]	Through liquidation of underlying investments
Interest in Limited Partnerships and Limited Liability Companies [Member] | CTE Drive, LLC [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value	[3]	$ 13
Redemption Frequency	[3]	Through liquidation of underlying investments
Interest in Limited Partnerships and Limited Liability Companies [Member] | Oakbrook Parkway LLC [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value	[3]	$ 25
Redemption Frequency	[3]	Through liquidation of underlying investments
Interest in Limited Partnerships and Limited Liability Companies [Member] | West Jefferson, LLC [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value	[3]	$ 26
Redemption Frequency	[3]	Through liquidation of underlying investments
Interest in Limited Partnerships and Limited Liability Companies [Member] | MacCorkle Ave SE, LLC [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value	[3]	$ 14
Redemption Frequency	[3]	Through liquidation of underlying investments
Interest in Limited Partnerships and Limited Liability Companies [Member] | S Pike Road West, LLC [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value	[3]	$ 1
Redemption Frequency	[3]	Through liquidation of underlying investments
Interest in Limited Partnerships and Limited Liability Companies [Member] | N US 131, LLC [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value	[3]	$ 1
Redemption Frequency	[3]	Through liquidation of underlying investments
Interest in Limited Partnerships and Limited Liability Companies [Member] | E Stockton Blvd, LLC [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair Value	[3]	$ 6
Redemption Frequency	[3]	Through liquidation of underlying investments

[1] The partnerships' investment objective is to seek capital appreciation principally through investing in investment funds managed by third party investment managers who employ a variety of alternative investment strategies. These instruments are subject to certain withdrawal restrictions. The Plan is in the process of liquidating its interest in the partnerships and distributions are expected to be made over the next four years.

[2] The fund's objective is to realize substantial long-term capital appreciation by investing in timberland properties primarily in South America and Australia. This investment is subject to certain withdrawal restrictions.

[3] The entity invests in commercial real estate properties that are leased to Frontier. The leases are triple net, whereby Frontier is responsible for all expenses, including but not limited to, insurance, repairs and maintenance and payment of property taxes.