Fair Value (Assets and Liabilities measured at fair value on a recurring basis) (Details) (USD $) In Millions, unless otherwise specified	Sep. 30, 2013	Dec. 31, 2012
Cash and cash equivalents	$ 8,286	$ 8,406
Available-for-sale Securities, Debt Securities	19,536
Available-for-sale Securities	808	677
Total assets at fair value	28,652	28,323
Debt Securities [Member]
Available-for-sale Securities, Debt Securities	19,536	19,226
U.S. Government and Agency Obligations [Member]
Available-for-sale Securities, Debt Securities	2,465	2,538
State and Municipal Obligations [Member]
Available-for-sale Securities, Debt Securities	6,750	6,667
Corporate Obligations [Member]
Available-for-sale Securities, Debt Securities	7,634	7,209
U.S. Agency Mortgage-Backed Securities [Member]
Available-for-sale Securities, Debt Securities	2,020	2,238
Non-U.S. Agency Mortgage-Backed Securities [Member]
Available-for-sale Securities, Debt Securities	667	574
Quoted Prices in Active Markets (Level 1) [Member]
Cash and cash equivalents	7,943	7,615
Available-for-sale Securities	536	450
Total assets at fair value	10,409	9,830
Quoted Prices in Active Markets (Level 1) [Member] | Debt Securities [Member]
Available-for-sale Securities, Debt Securities	1,930	1,765
Quoted Prices in Active Markets (Level 1) [Member] | U.S. Government and Agency Obligations [Member]
Available-for-sale Securities, Debt Securities	1,899	1,752
Quoted Prices in Active Markets (Level 1) [Member] | State and Municipal Obligations [Member]
Available-for-sale Securities, Debt Securities	0	0
Quoted Prices in Active Markets (Level 1) [Member] | Corporate Obligations [Member]
Available-for-sale Securities, Debt Securities	31	13
Quoted Prices in Active Markets (Level 1) [Member] | U.S. Agency Mortgage-Backed Securities [Member]
Available-for-sale Securities, Debt Securities	0	0
Quoted Prices in Active Markets (Level 1) [Member] | Non-U.S. Agency Mortgage-Backed Securities [Member]
Available-for-sale Securities, Debt Securities	0	0
Other Observable Inputs (Level 2) [Member]
Cash and cash equivalents	343	791
Available-for-sale Securities	26	3
Total assets at fair value	17,964	18,252
Other Observable Inputs (Level 2) [Member] | Debt Securities [Member]
Available-for-sale Securities, Debt Securities	17,573	17,444
Other Observable Inputs (Level 2) [Member] | U.S. Government and Agency Obligations [Member]
Available-for-sale Securities, Debt Securities	566	786
Other Observable Inputs (Level 2) [Member] | State and Municipal Obligations [Member]
Available-for-sale Securities, Debt Securities	6,750	6,667
Other Observable Inputs (Level 2) [Member] | Corporate Obligations [Member]
Available-for-sale Securities, Debt Securities	7,576	7,185
Other Observable Inputs (Level 2) [Member] | U.S. Agency Mortgage-Backed Securities [Member]
Available-for-sale Securities, Debt Securities	2,020	2,238
Other Observable Inputs (Level 2) [Member] | Non-U.S. Agency Mortgage-Backed Securities [Member]
Available-for-sale Securities, Debt Securities	661	568
Fair Value, Measurements, Recurring [Member] | AARP Program [Member]
Cash and cash equivalents	227	230
Available-for-sale Securities	4	3
Total assets at fair value	2,694	2,773
Other liabilities	26	81
Fair Value, Measurements, Recurring [Member] | AARP Program [Member] | Debt Securities [Member]
Available-for-sale Securities, Debt Securities	2,463	2,540
Fair Value, Measurements, Recurring [Member] | AARP Program [Member] | U.S. Government and Agency Obligations [Member]
Available-for-sale Securities, Debt Securities	758	789
Fair Value, Measurements, Recurring [Member] | AARP Program [Member] | State and Municipal Obligations [Member]
Available-for-sale Securities, Debt Securities	61	51
Fair Value, Measurements, Recurring [Member] | AARP Program [Member] | Corporate Obligations [Member]
Available-for-sale Securities, Debt Securities	1,077	1,118
Fair Value, Measurements, Recurring [Member] | AARP Program [Member] | U.S. Agency Mortgage-Backed Securities [Member]
Available-for-sale Securities, Debt Securities	428	427
Fair Value, Measurements, Recurring [Member] | AARP Program [Member] | Non-U.S. Agency Mortgage-Backed Securities [Member]
Available-for-sale Securities, Debt Securities	139	155
Fair Value, Measurements, Recurring [Member] | AARP Program [Member] | Quoted Prices in Active Markets (Level 1) [Member]
Cash and cash equivalents	227	230
Available-for-sale Securities	0	0
Total assets at fair value	714	775
Other liabilities	8	23
Fair Value, Measurements, Recurring [Member] | AARP Program [Member] | Quoted Prices in Active Markets (Level 1) [Member] | Debt Securities [Member]
Available-for-sale Securities, Debt Securities	487	545
Fair Value, Measurements, Recurring [Member] | AARP Program [Member] | Quoted Prices in Active Markets (Level 1) [Member] | U.S. Government and Agency Obligations [Member]
Available-for-sale Securities, Debt Securities	487	545
Fair Value, Measurements, Recurring [Member] | AARP Program [Member] | Quoted Prices in Active Markets (Level 1) [Member] | State and Municipal Obligations [Member]
Available-for-sale Securities, Debt Securities	0	0
Fair Value, Measurements, Recurring [Member] | AARP Program [Member] | Quoted Prices in Active Markets (Level 1) [Member] | Corporate Obligations [Member]
Available-for-sale Securities, Debt Securities	0	0
Fair Value, Measurements, Recurring [Member] | AARP Program [Member] | Quoted Prices in Active Markets (Level 1) [Member] | U.S. Agency Mortgage-Backed Securities [Member]
Available-for-sale Securities, Debt Securities	0	0
Fair Value, Measurements, Recurring [Member] | AARP Program [Member] | Quoted Prices in Active Markets (Level 1) [Member] | Non-U.S. Agency Mortgage-Backed Securities [Member]
Available-for-sale Securities, Debt Securities	0	0
Fair Value, Measurements, Recurring [Member] | AARP Program [Member] | Other Observable Inputs (Level 2) [Member]
Cash and cash equivalents	0	0
Available-for-sale Securities	4	3
Total assets at fair value	1,980	1,998
Other liabilities	18	58
Fair Value, Measurements, Recurring [Member] | AARP Program [Member] | Other Observable Inputs (Level 2) [Member] | Debt Securities [Member]
Available-for-sale Securities, Debt Securities	1,976	1,995
Fair Value, Measurements, Recurring [Member] | AARP Program [Member] | Other Observable Inputs (Level 2) [Member] | U.S. Government and Agency Obligations [Member]
Available-for-sale Securities, Debt Securities	271	244
Fair Value, Measurements, Recurring [Member] | AARP Program [Member] | Other Observable Inputs (Level 2) [Member] | State and Municipal Obligations [Member]
Available-for-sale Securities, Debt Securities	61	51
Fair Value, Measurements, Recurring [Member] | AARP Program [Member] | Other Observable Inputs (Level 2) [Member] | Corporate Obligations [Member]
Available-for-sale Securities, Debt Securities	1,077	1,118
Fair Value, Measurements, Recurring [Member] | AARP Program [Member] | Other Observable Inputs (Level 2) [Member] | U.S. Agency Mortgage-Backed Securities [Member]
Available-for-sale Securities, Debt Securities	428	427
Fair Value, Measurements, Recurring [Member] | AARP Program [Member] | Other Observable Inputs (Level 2) [Member] | Non-U.S. Agency Mortgage-Backed Securities [Member]
Available-for-sale Securities, Debt Securities	$ 139	$ 155