1.0.0.3 true Consolidated Statements of Capitalization (Parenthetical) (USD $) In Millions, except Share data, unless otherwise specified false 1 $ false false Pure Standard http://www.xbrl.org/2003/instance pure xbrli 0 Shares Standard http://www.xbrl.org/2003/instance shares xbrli 0 USD Standard http://www.xbrl.org/2003/iso4217 USD iso4217 0 false 2 $ false false Pure Standard http://www.xbrl.org/2003/instance pure xbrli 0 Shares Standard http://www.xbrl.org/2003/instance shares xbrli 0 USD Standard http://www.xbrl.org/2003/iso4217 USD iso4217 0 7 Common stock, Par value 2 us-gaap_CommonStockParOrStatedValuePerShare us-gaap true na instant decimal No definition available. false false false false false false false false false 1 false true 5 5 false false 2 false true 5 5 false false No definition available. No authoritative reference available. false 8 Common stock, shares Authorized 2 us-gaap_CommonStockSharesAuthorized us-gaap true na instant shares No definition available. false false false false false false false false false 1 false true 1000000000 1000000000.00 false false 2 false true 1000000000 1000000000.00 false false No definition available. No authoritative reference available. false 9 Common stock, shares Issued 2 us-gaap_CommonStockSharesIssued us-gaap true na instant shares No definition available. false false false false false false false false false 1 false true 820000000 820000000.00 false false 2 false true 778000000 778000000.00 false false No definition available. No authoritative reference available. false 10 Treasury shares 2 us-gaap_TreasuryStockShares us-gaap true na instant shares No definition available. false false false false false false false false false 1 false true 500000 500000.00 false false 2 false true 400000 400000.00 false false No definition available. No authoritative reference available. false 11 Annual interest requirement 2 so_AnnualizedInterestLongTermDebt so false credit instant monetary Represents the interest expected to be incurred during the next twelve months on long-term debt. false false false false false false false false false 1 true true 894000000 894 false false 2 false false 0 0 false false Represents the interest expected to be incurred during the next twelve months on long-term debt. No authoritative reference available. false 12 Annual dividend requirement 2 so_AnnualDividendPreferredAndPreferenceStock so false credit instant monetary Represents the dividend expected to be paid during the next twelve months to preferred and/or preference stockholders. false false false false false false false false false 1 false true 45000000 45 false false 2 false false 0 0 false false Represents the dividend expected to be paid during the next twelve months to preferred and/or preference stockholders. No authoritative reference available. false 15 Preference stock 0 na true na na na No definition available. false true false false false false false false false 1 false false 0 0 false false 2 false false 0 0 false false No definition available. No authoritative reference available. false 16 Preferred Stock, Par or Stated Value Per Share 2 us-gaap_PreferredStockParOrStatedValuePerShare us-gaap true na instant decimal No definition available. false false false false false false false false false 1 false true 1 1 false false 2 false true 1 1 false false No definition available. No authoritative reference available. false 19 Preferred Stock, Shares Authorized 2 us-gaap_PreferredStockSharesAuthorized us-gaap true na instant shares No definition available. false false false false false false false false false 1 false true 65000000 65000000.00 false false 2 false true 65000000 65000000.00 false false No definition available. No authoritative reference available. false 20 Preferred Stock, Shares Outstanding 2 us-gaap_PreferredStockSharesOutstanding us-gaap true na instant shares No definition available. false false false false false false false false false 1 false true 14000000 14000000.00 false false 2 false true 14000000 14000000.00 false false No definition available. No authoritative reference available. false 29 Redeemable Preferred Stock, $1 par value 0 na true na na na No definition available. false true false false false false false false false 1 false false 0 0 false false 2 false false 0 0 false false No definition available. No authoritative reference available. false 30 Preferred Stock, Par or Stated Value Per Share 2 us-gaap_PreferredStockParOrStatedValuePerShare us-gaap true na instant decimal No definition available. false false false false false false false false false 1 false true 1 1 false false 2 false true 1 1 false false No definition available. No authoritative reference available. false 31 Redeemable Cumulative preferred stock, Authorized 2 us-gaap_RedeemablePreferredStockSharesAuthorized us-gaap true na instant shares No definition available. false false false false false false false false false 1 false true 28000000 28000000.00 false false 2 false true 28000000 28000000.00 false false No definition available. No authoritative reference available. false 32 Redeemable Cumulative preferred stock, Outstanding 2 us-gaap_RedeemablePreferredStockSharesOutstanding us-gaap true na instant shares No definition available. false false false false false false false false false 1 false true 12000000 12000000.00 false false 2 false true 12000000 12000000.00 false false No definition available. No authoritative reference available. false 40 Annual dividend requirement 2 so_AnnualDividendPreferredAndPreferenceStock so false credit instant monetary Represents the dividend expected to be paid during the next twelve months to preferred and/or preference stockholders. false false false false false false false false false 1 true true 20000000 20 false false 2 false false 0 0 false false Represents the dividend expected to be paid during the next twelve months to preferred and/or preference stockholders. No authoritative reference available. false 43 Redeemable Preferred Stock, $1 par value | Cumulative Preferred Stock 0 na true na na na No definition available. false true false false false false false false false 1 false false 0 0 false false 2 false false 0 0 false false No definition available. No authoritative reference available. false 55 Dividend Rate, Minimum 2 so_PreferredStockDividendRateStatedPercentageRateRangeMinimum so false na duration pure Preferred Stock Dividend Rate Stated Percentage Rate Range Minimum. false false false false false false false false false 1 false true 0.0495 0.0495 false false 2 false true 0.0495 0.0495 false false Preferred Stock Dividend Rate Stated Percentage Rate Range Minimum. No authoritative reference available. false 56 Dividend Rate, Maximum 2 so_PreferredStockDividendRateStatedPercentageRateRangeMaximum so false na duration pure Preferred Stock Dividend Rate Stated Percentage Rate Range Maximum. false false false false false false false false false 1 false true 0.0583 0.0583 false false 2 false true 0.0583 0.0583 false false Preferred Stock Dividend Rate Stated Percentage Rate Range Maximum. No authoritative reference available. false 57 Redeemable Preferred Stock, $25 stated value 0 na true na na na No definition available. false true false false false false false false false 1 false false 0 0 false false 2 false false 0 0 false false No definition available. No authoritative reference available. false 58 Preferred Stock, Par or Stated Value Per Share 2 us-gaap_PreferredStockParOrStatedValuePerShare us-gaap true na instant decimal No definition available. false false false false false false false false false 1 false true 25 25 false false 2 false true 25 25 false false No definition available. No authoritative reference available. false 71 Redeemable Preferred Stock, $100 par or stated value 0 na true na na na No definition available. false true false false false false false false false 1 false false 0 0 false false 2 false false 0 0 false false No definition available. No authoritative reference available. false 72 Preferred Stock, Par or Stated Value Per Share 2 us-gaap_PreferredStockParOrStatedValuePerShare us-gaap true na instant decimal No definition available. false false false false false false false false false 1 false true 100 100 false false 2 false true 100 100 false false No definition available. No authoritative reference available. false 73 Redeemable Cumulative preferred stock, Authorized 2 us-gaap_RedeemablePreferredStockSharesAuthorized us-gaap true na instant shares No definition available. false false false false false false false false false 1 false true 20000000 20000000.00 false false 2 false true 20000000 20000000.00 false false No definition available. No authoritative reference available. false 74 Redeemable Cumulative preferred stock, Outstanding 2 us-gaap_RedeemablePreferredStockSharesOutstanding us-gaap true na instant shares No definition available. false false false false false false false false false 1 false true 1000000 1000000.00 false false 2 false true 1000000 1000000.00 false false No definition available. No authoritative reference available. false 85 Redeemable Preferred Stock, $100 par or stated value | Cumulative Preferred Stock 0 na true na na na No definition available. false true false false false false false false false 1 false false 0 0 false false 2 false false 0 0 false false No definition available. No authoritative reference available. false 97 Dividend Rate, Minimum 2 so_PreferredStockDividendRateStatedPercentageRateRangeMinimum so false na duration pure Preferred Stock Dividend Rate Stated Percentage Rate Range Minimum. false false false false false false false false false 1 false true 0.042 0.042 false false 2 false true 0.042 0.042 false false Preferred Stock Dividend Rate Stated Percentage Rate Range Minimum. No authoritative reference available. false 98 Dividend Rate, Maximum 2 so_PreferredStockDividendRateStatedPercentageRateRangeMaximum so false na duration pure Preferred Stock Dividend Rate Stated Percentage Rate Range Maximum. false false false false false false false false false 1 false true 0.0544 0.0544 false false 2 false true 0.0544 0.0544 false false Preferred Stock Dividend Rate Stated Percentage Rate Range Maximum. No authoritative reference available. false 99 Preference Stock, $100 par or stated value 0 na true na na na No definition available. false true false false false false false false false 1 false false 0 0 false false 2 false false 0 0 false false No definition available. No authoritative reference available. false 100 Preferred Stock, Par or Stated Value Per Share 2 us-gaap_PreferredStockParOrStatedValuePerShare us-gaap true na instant decimal No definition available. false false false false false false false false false 1 false true 100 100 false false 2 false true 100 100 false false No definition available. No authoritative reference available. false 104 Preferred Stock, Shares Outstanding 2 us-gaap_PreferredStockSharesOutstanding us-gaap true na instant shares No definition available. false false false false false false false false false 1 false true 3000000 3000000.00 false false 2 false true 3000000 3000000.00 false false No definition available. No authoritative reference available. false 111 Dividend Rate, Minimum 2 so_PreferredStockDividendRateStatedPercentageRateRangeMinimum so false na duration pure Preferred Stock Dividend Rate Stated Percentage Rate Range Minimum. false false false false false false false false false 1 false true 0.06 0.06 false false 2 false true 0.06 0.06 false false Preferred Stock Dividend Rate Stated Percentage Rate Range Minimum. No authoritative reference available. false 112 Dividend Rate, Maximum 2 so_PreferredStockDividendRateStatedPercentageRateRangeMaximum so false na duration pure Preferred Stock Dividend Rate Stated Percentage Rate Range Maximum. false false false false false false false false false 1 false true 0.065 0.065 false false 2 false true 0.065 0.065 false false Preferred Stock Dividend Rate Stated Percentage Rate Range Maximum. No authoritative reference available. false 113 Preference Stock, $1 par value 0 na true na na na No definition available. false true false false false false false false false 1 false false 0 0 false false 2 false false 0 0 false false No definition available. No authoritative reference available. false 125 Dividend Rate, Minimum 2 so_PreferredStockDividendRateStatedPercentageRateRangeMinimum so false na duration pure Preferred Stock Dividend Rate Stated Percentage Rate Range Minimum. false false false false false false false false false 1 false true 0.0563 0.0563 false false 2 false true 0.0563 0.0563 false false Preferred Stock Dividend Rate Stated Percentage Rate Range Minimum. No authoritative reference available. false 126 Dividend Rate, Maximum 2 so_PreferredStockDividendRateStatedPercentageRateRangeMaximum so false na duration pure Preferred Stock Dividend Rate Stated Percentage Rate Range Maximum. false false false false false false false false false 1 false true 0.065 0.065 false false 2 false true 0.065 0.065 false false Preferred Stock Dividend Rate Stated Percentage Rate Range Maximum. No authoritative reference available. false 127 Noncumulative Preferred Stock 0 na true na na na No definition available. false true false false false false false false false 1 false false 0 0 false false 2 false false 0 0 false false No definition available. No authoritative reference available. false 128 Preferred Stock, Par or Stated Value Per Share 2 us-gaap_PreferredStockParOrStatedValuePerShare us-gaap true na instant decimal No definition available. false false false false false false false false false 1 false true 25 25 false false 2 false true 25 25 false false No definition available. No authoritative reference available. false 131 Preferred Stock, Shares Authorized 2 us-gaap_PreferredStockSharesAuthorized us-gaap true na instant shares No definition available. false false false false false false false false false 1 false true 60000000 60000000.00 false false 2 false true 60000000 60000000.00 false false No definition available. No authoritative reference available. false 132 Preferred Stock, Shares Outstanding 2 us-gaap_PreferredStockSharesOutstanding us-gaap true na instant shares No definition available. false false false false false false false false false 1 false true 2000000 2000000.00 false false 2 false true 2000000 2000000.00 false false No definition available. No authoritative reference available. false 139 Dividend Rate, Minimum 2 so_PreferredStockDividendRateStatedPercentageRateRangeMinimum so false na duration pure Preferred Stock Dividend Rate Stated Percentage Rate Range Minimum. false false false false false false false false false 1 false true 0.06 0.06 false false 2 false true 0.06 0.06 false false Preferred Stock Dividend Rate Stated Percentage Rate Range Minimum. No authoritative reference available. false 140 Dividend Rate, Maximum 2 so_PreferredStockDividendRateStatedPercentageRateRangeMaximum so false na duration pure Preferred Stock Dividend Rate Stated Percentage Rate Range Maximum. false false false false false false false false false 1 false true 0.0613 0.0613 false false 2 false true 0.0613 0.0613 false false Preferred Stock Dividend Rate Stated Percentage Rate Range Maximum. No authoritative reference available. false false 2 41 false Millions NoRounding UnKnown true true