Long-Term Debt (Debt Issuances) (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2013 Thirty Years [Member] Mortgages [Member]	Mar. 31, 2013 Thirty Years [Member] Mortgages [Member]	Dec. 31, 2013 Eleven Years [Member] Mortgages [Member]	Aug. 31, 2013 Eleven Years [Member] Mortgages [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage		4.00%		3.65%
Debt Instrument, Face Amount	$ 775		$ 375		$ 400